HLS: Fix on_hls and hls_dispose critical zone issue. v5.0.174 v6.0.69 (#3781)

on_hls and hls_dispose are two coroutines, with potential race
conditions. That is, during on_hls, if the API Server being accessed is
slower, it will switch to the hls_dispose coroutine to start cleaning
up. However, when the API Server is processing the slice, a situation
may occur where the slice does not exist, resulting in the following
log:

```
[2023-08-22 12:03:20.309][WARN][40][x5l48q7b][11] ignore task failed code=4005(HttpStatus)(Invalid HTTP status code) : callback on_hls http://localhost:2024/terraform/v1/hooks/srs/hls : http: post http://localhost:2024/terraform/v1/hooks/srs/hls with {"server_id":"vid-5d7dxn8","service_id":"cu153o7g","action":"on_hls","client_id":"x5l48q7b","ip":"172.17.0.1","vhost":"__defaultVhost__","app":"live","tcUrl":"srt://172.17.0.2/live","stream":"stream-44572-2739617660809856576","param":"secret=1ed8e0ffbc53439c8fc8da30ab8c19f0","duration":4.57,"cwd":"/usr/local/srs-stack/platform","file":"./objs/nginx/html/live/stream-44572-2739617660809856576-1.ts","url":"live/stream-44572-2739617660809856576-1.ts","m3u8":"./objs/nginx/html/live/stream-44572-2739617660809856576.m3u8","m3u8_url":"live/stream-44572-2739617660809856576.m3u8","seq_no":1,"stream_url":"/live/stream-44572-2739617660809856576","stream_id":"vid-0n9zoz3"}, status=500, res=invalid ts file ./objs/nginx/html/live/stream-44572-2739617660809856576-1.ts: stat ./objs/nginx/html/live/stream-44572-2739617660809856576-1.ts: no such file or directory
thread [40][x5l48q7b]: call() [./src/app/srs_app_hls.cpp:122][errno=11]
thread [40][x5l48q7b]: on_hls() [./src/app/srs_app_http_hooks.cpp:401][errno=11]
thread [40][x5l48q7b]: do_post() [./src/app/srs_app_http_hooks.cpp:638][errno=11]

[error] 2023/08/22 12:03:20.076984 [52][1001] Serve /terraform/v1/hooks/srs/hls failed, err is stat ./objs/nginx/html/live/stream-44572-2739617660809856576-1.ts: no such file or directory
invalid ts file ./objs/nginx/html/live/stream-44572-2739617660809856576-1.ts
main.handleOnHls.func1.1
	/g/platform/srs-hooks.go:684
main.handleOnHls.func1
	/g/platform/srs-hooks.go:720
net/http.HandlerFunc.ServeHTTP
	/usr/local/go/src/net/http/server.go:2084
net/http.(*ServeMux).ServeHTTP
	/usr/local/go/src/net/http/server.go:2462
net/http.serverHandler.ServeHTTP
	/usr/local/go/src/net/http/server.go:2916
net/http.(*conn).serve
	/usr/local/go/src/net/http/server.go:1966
runtime.goexit
	/usr/local/go/src/runtime/asm_amd64.s:1571
```

Similarly, when stopping the stream, on_hls will also be called to
handle the last slice. If the API Server is slower at this time, it will
enter hls_dispose and call unpublish repeatedly. Since the previous
unpublish is still blocked in on_hls, the following interference log
will appear:

```
[2023-08-22 12:03:18.748][INFO][40][6498088c] hls cycle to dispose hls /live/stream-44572-2739617660809856576, timeout=10000000ms
[2023-08-22 12:03:18.752][WARN][40][6498088c][115] flush audio ignored, for segment is not open.
[2023-08-22 12:03:18.752][WARN][40][6498088c][115] ignore the segment close, for segment is not open.
```

Although this log will not cause problems, it can interfere with
judgment.

The solution is to add an 'unpublishing' status. If it is in the
'unpublishing' status, then do not clean up the slices.

---------

Co-authored-by: Haibo Chen <495810242@qq.com>

trunk/src/app/srs_app_hls.hpp

@@ -279,10 +279,12 @@ private:
     bool enabled;
     // Whether the HLS stream is able to be disposed.
     bool disposable;
+    // Whether the HLS stream is unpublishing.
+    bool unpublishing_;
     // Whether requires HLS to do reload asynchronously.
     bool async_reload_;
     bool reloading_;
-    // To detect heartbeat and dipose it if configured.
+    // To detect heartbeat and dispose it if configured.
     srs_utime_t last_update_time;
 private:
     // If the diff=dts-previous_audio_dts is about 23,