Crash in validate mode on regex matches in routes since 1.23

*Title*: Crash in validate mode on regex matches in routes since 1.23

*Description*:
Hi,

We’ve identified a crash that occurs in validate mode (and only validate mode) when a route includes a regex match against a header. There appears to be no issue when mode is set to ‘serve’. Please find attached a static config and a Dockerfile (with the same config baked in) for reproduction.

We’ve tested this case in various versions and it appears to have been introduced in 1.23 and remains present in all current 1.24 releases.

Any other kind of string matcher works, and the deprecated google_re2 matcher also works (with the expected deprecation warning). The only issue appears to be the new ‘regex’ option introduced in 1.23.0

Dockerfile:
```bash
FROM envoyproxy/envoy:v1.24.1

RUN echo 'static_resources:\n\
listeners:\n\
- address:\n\
socket_address:\n\
address: "127.0.0.1"\n\
port_value: 80\n\
filter_chains:\n\
filters:\n\
- name: envoy.http_connection_manager\n\
typed_config:\n\
"@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager\n\
stat_prefix: example\n\
route_config:\n\
name: demo\n\
virtual_hosts:\n\
- name: default\n\
domains:\n\
- "*"\n\
routes:\n\
- match:\n\
prefix: "/"\n\
headers:\n\
- name: "X-Whatever"\n\
string_match:\n\
safe_regex:\n\
regex: ".*"\n\
direct_response:\n\
status: 200' > /etc/envoy/envoy.yaml

CMD ["envoy", "-c", "/etc/envoy/envoy.yaml", "--mode", "validate"]
```

Sample envoy template:
```
static_resources:
listeners:
- address:
socket_address:
address: "127.0.0.1"
port_value: 80
filter_chains:
filters:
- name: envoy.http_connection_manager
typed_config:
"@type": type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager
stat_prefix: example
route_config:
name: demo
virtual_hosts:
- name: default
domains:
- "*"
routes:
- match:
prefix: "/"
headers:
- name: "X-Whatever"
string_match:
safe_regex:
regex: ".*"
direct_response:
status: 200
```

Sample output from the issue:

```bash
[2022-12-22 16:33:56.805][1][info][main] [source/server/server.cc:808] runtime: {}
[2022-12-22 16:33:56.805][1][info][config] [source/server/configuration_impl.cc:131] loading tracing configuration
[2022-12-22 16:33:56.805][1][info][config] [source/server/configuration_impl.cc:91] loading 0 static secret(s)
[2022-12-22 16:33:56.805][1][info][config] [source/server/configuration_impl.cc:97] loading 0 cluster(s)
[2022-12-22 16:33:56.806][1][info][config] [source/server/configuration_impl.cc:101] loading 1 listener(s)
[2022-12-22 16:33:56.807][1][critical][assert] [./source/common/singleton/threadsafe_singleton.h:56] assert failure: loader_ != nullptr. Details: InjectableSingleton used prior to initialization
[2022-12-22 16:33:56.807][1][critical][backtrace] [./source/server/backtrace.h:104] Caught Aborted, suspect faulting address 0x6500000001
[2022-12-22 16:33:56.807][1][critical][backtrace] [./source/server/backtrace.h:91] Backtrace (use tools/stack_decode.py to get line numbers):
[2022-12-22 16:33:56.807][1][critical][backtrace] [./source/server/backtrace.h:92] Envoy version: 69958e4fe32da561376d8b1d367b5e6942dfba24/1.24.1/Clean/RELEASE/BoringSSL
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:96] #0: __kernel_rt_sigreturn [0xffffa3cf0790]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:96] #1: abort [0xffffa3a65aac]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #2: [0xaaaad48524e0]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #3: [0xaaaad4851bd4]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #4: [0xaaaad62e407c]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #5: [0xaaaad4974ad8]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #6: [0xaaaad6060e4c]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #7: [0xaaaad6068c00]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #8: [0xaaaad607f42c]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #9: [0xaaaad606a740]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #10: [0xaaaad6069d64]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #11: [0xaaaad606b8e8]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #12: [0xaaaad606d350]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #13: [0xaaaad5fc1e5c]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #14: [0xaaaad5fc8e78]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #15: [0xaaaad5fbcd14]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #16: [0xaaaad5fc03c0]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #17: [0xaaaad5fc77b4]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #18: [0xaaaad5fbe6e4]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #19: [0xaaaad5fbc9c4]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #20: [0xaaaad5f37a50]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #21: [0xaaaad5f36504]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #22: [0xaaaad5ed1438]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #23: [0xaaaad5edb350]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #24: [0xaaaad5edafb0]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #25: [0xaaaad5ee3d88]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #26: [0xaaaad5ec3c54]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #27: [0xaaaad5ed6da0]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #28: [0xaaaad5ed6028]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #29: [0xaaaad5f2b7f0]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #30: [0xaaaad5acdbe8]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #31: [0xaaaad5accd58]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #32: [0xaaaad5acc24c]
[2022-12-22 16:33:56.808][1][critical][backtrace] [./source/server/backtrace.h:98] #33: [0xaaaad46f02e4]
[2022-12-22 16:33:56.809][1][critical][backtrace] [./source/server/backtrace.h:98] #34: [0xaaaad46f09c8]
[2022-12-22 16:33:56.809][1][critical][backtrace] [./source/server/backtrace.h:98] #35: [0xaaaad46ed13c]
[2022-12-22 16:33:56.809][1][critical][backtrace] [./source/server/backtrace.h:96] #36: __libc_start_main [0xffffa3a65e10]
```