H3 doh Accidental empty parsing response

carry out. /dnsproxy-l 0.0.0.0-p 5355-u h3://doh---------------.com/dns-query -b 223.5.5.5 -v

```
2023/04/18 11:15:31 120876#75 [debug] dnsproxy: cache: disabled; not caching
2023/04/18 11:15:31 120876#75 [debug] https://doh-------------: sending request A baidu.com.
2023/04/18 11:15:31 120876#75 [debug] https://doh-------------: response: requesting https://doh----------------------: Get_0rtt "https://doh---------------?dns=AAABIAABAAAAAAABBWtic21sA2NvbQAAAQABAAApEAAAAAAAABcACAAHAAEYANOLBQAKAAj0ol95vywyUw": Application error 0x100 (remote): keepalive timeout
2023/04/18 11:15:31 120876#75 [debug] re-creating the http client due to requesting https://doh------------------: Get_0rtt "https://doh--------------------?dns=AAABIAABAAAAAAABBWtic21sA2NvbQAAAQABAAApEAAAAAAAABcACAAHAAEYANOLBQAKAAj0ol95vywyUw": Application error 0x100 (remote): keepalive timeout
2023/04/18 11:15:31 120876#75 [debug] github.com/AdguardTeam/dnsproxy/upstream.(*bootstrapper).createDialContext.func1(): Dialing to ip:443
2023/04/18 11:15:31 120876#75 [debug] github.com/AdguardTeam/dnsproxy/upstream.(*bootstrapper).createDialContext.func1(): dialer has successfully initialized connection to ip:443 in 29.358μs
2023/04/18 11:15:31 120876#75 [debug] using HTTP/3 for this upstream: QUIC was faster
2023/04/18 11:15:31 120876#75 [debug] github.com/AdguardTeam/dnsproxy/proxy.exchangeWithUpstream(): upstream https://doh------------------ failed to exchange ;baidu.com. IN A in 299.933μs. Cause: requesting https://doh-------------: Get_0rtt "https://dog--------------?dns=AAABIAABAAAAAAABBWtic21sA2NvbQAAAQABAAApEAAAAAAAABcACAAHAAEYANOLBQAKAAj0ol95vywyUw": Application error 0x100 (remote): keepalive timeout
2023/04/18 11:15:31 120876#75 [debug] github.com/AdguardTeam/dnsproxy/proxy.(*Proxy).replyFromUpstream(): RTT: 324.708μs
2023/04/18 11:15:31 120876#75 [debug] github.com/AdguardTeam/dnsproxy/proxy.(*Proxy).logDNSMessage(): OUT: ;; opcode: QUERY, status: SERVFAIL, id: 61611
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;baidu.com. IN A

2023/04/18 11:15:31 120876#75 [debug] github.com/AdguardTeam/dnsproxy/proxy.(*Proxy).udpHandlePacket(): error handling DNS (udp) request: talking to dns upstream: requesting https://doh--------------: Get_0rtt "https://doh------------------?dns=AAABIAABAAAAAAABBWtic21sA2NvbQAAAQABAAApEAAAAAAAABcACAAHAAEYANOLBQAKAAj0ol95vywyUw": Application error 0x100 (remote): keepalive timeout
2023/04/18 11:19:48 120876#23 [debug] github.com/AdguardTeam/dnsproxy/proxy.(*Proxy).udpHandlePacket(): Start handling new UDP packet from 127.0.0.1:42750
2023/04/18 11:19:48 120876#23 [debug] github.com/AdguardTeam/dnsproxy/proxy.(*Proxy).logDNSMessage(): IN: ;; opcode: QUERY, status: NOERROR, id: 24909
;; flags: rd ad; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version 0; flags: ; udp: 4096
; SUBNET: 211.139.5.0/24/0
; COOKIE: f1bcfafb6ee6de42

;; QUESTION SECTION:
;baidu.com. IN A

```

Reproduce the command shown in the issue and review the logged DoH/HTTP/3 upstream exchange, including the keepalive timeout and empty response. The report names no source files, tests, expected behavior, or acceptance criteria, so the intended fix and completion check need clarification first.

由索引模型根据 Issue 内容生成。