Witness_node crashes on exit

**Bug Description**

Plugins enabled: `plugins="witness market_history"`
Logs:
```
444163ms th_a application.cpp:678 handle_block ] Got block: #76156912 048a0ff0c9325486a689eb4ab080d4c10e3fbb58 time: 2023-01-23T09:07:24 transaction(s): 1 latency: 163 ms from: roelandp irreversible: 76156893 (-19)
445105ms th_a application.cpp:740 handle_transaction ] Got 1 transactions from network
446185ms fc::asio main.cpp:214 operator() ] Caught SIGINT, attempting to exit cleanly
446186ms th_a main.cpp:234 main ] Exiting from signal 2
446192ms th_a application.cpp:1169 ~application ] Application quitting
446193ms th_a application.cpp:1080 shutdown ] Shutting down application
446197ms th_a application.cpp:1088 shutdown ] Shutting down plugins
446212ms th_a stacktrace.cpp:45 segfault_signal_hand ] 0# 0x000055E5F834856C in ./witness_node.6.1.0
1# 0x00007FEE2E359090 in /lib/x86_64-linux-gnu/libc.so.6
2# graphene::app::detail::application_impl::shutdown_plugins() const in ./witness_node.6.1.0
3# graphene::app::detail::application_impl::shutdown() in ./witness_node.6.1.0
4# graphene::app::application::~application() in ./witness_node.6.1.0
5# 0x000055E5F7A7C87E in ./witness_node.6.1.0
6# main in ./witness_node.6.1.0
7# __libc_start_main in /lib/x86_64-linux-gnu/libc.so.6
8# _start in ./witness_node.6.1.0

./start_witness_node.sh: line 2: 1337 Aborted (core dumped) ./witness_node.6.1.0 --enable-standby-votes-tracking=false --p2p-endpoint="0.0.0.0:1776" --rpc-endpoint="127.0.0.1:8090" --plugins="witness market_history" --ignore-api-helper-indexes-warning --required-participation=0
```

**Impacts**
Describe which portion(s) of BitShares Core may be impacted by this bug. Please tick at least one box.
- [ ] API (the application programming interface)
- [ ] Build (the build process or something prior to compiled code)
- [ ] CLI (the command line wallet)
- [ ] Deployment (the deployment process after building such as Docker, Travis, etc.)
- [ ] DEX (the Decentralized EXchange, market engine, etc.)
- [ ] P2P (the peer-to-peer network for transaction/block propagation)
- [ ] Performance (system or user efficiency, etc.)
- [ ] Protocol (the blockchain logic, consensus, validation, etc.)
- [ ] Security (the security of system or user data, etc.)
- [ ] UX (the User Experience)
- [ ] Other (please add below)

**Host Environment**
Please provide details about the host environment. Much of this information can be found running: `witness_node --version`.
- Host OS: Ubuntu 20.04.5 LTS
- Host Physical RAM 8GB
- BitShares Version: 6.1.0
- OpenSSL Version: 1.1.1s
- Boost Version: 1.65.1

**Additional Context (optional)**
The `witness_node` binary is downloaded from the release page.

## CORE TEAM TASK LIST
- [ ] Evaluate / Prioritize Bug Report
- [ ] Refine User Stories / Requirements
- [ ] Define Test Cases
- [ ] Design / Develop Solution
- [ ] Perform QA/Testing
- [ ] Update Documentation

Start with the shutdown path shown in application.cpp, especially shutdown_plugins and shutdown, and reproduce the SIGINT exit using the listed witness_node version and plugins. Trace the crash reported through stacktrace.cpp and verify that witness_node shuts down cleanly without aborting or producing a segmentation fault.

Written by the indexing model from the issue text.