….0.171 (#4432)

Fixes a critical heap-use-after-free crash in HTTP-FLV streaming that
occurs when a client requests a stream while it's being unmounted
asynchronously.

- **Issue**: #4429 - Heap-use-after-free crash in
`SrsLiveStream::serve_http()`
- **Root Cause**: Race condition between coroutines in single-threaded
SRS server:
1. **Coroutine A**: HTTP client requests FLV stream → `serve_http()`
starts
2. **Coroutine B**: RTMP publisher disconnects → triggers async stream
destruction
3. **Async Worker**: Destroys `SrsLiveStream` object while Coroutine A
is yielded
  4. **Coroutine A**: Resumes and accesses freed memory → **CRASH**

1. **Early viewer registration**: Add HTTP connection to `viewers_` list
immediately in `serve_http()` before any I/O operations that could yield
2. **Lifecycle protection**: Split `serve_http()` into wrapper and
implementation to ensure proper viewer management
3. **Stream availability checks**: Add fast checks for stream disposal
state before critical operations
4. **Improved error handling**: Convert warnings to fatal errors when
trying to free alive streams

- **`SrsLiveStream::serve_http()`**: Now immediately registers viewer
and delegates to `serve_http_impl()`
- **`SrsLiveStream::serve_http_impl()`**: Contains the actual HTTP
serving logic
- **`SrsHttpStreamDestroy::call()`**: Enhanced error handling and longer
wait timeout
- **Stream state validation**: Added checks for `entry->enabled` before
proceeding with stream operations

Fixes #4429