When a client polls the HLS playlist (e.g. live.m3u8) after a live stream has
been disposed because its consumer count dropped to zero,
GetLiveStreamWithDirectStreamProvider returns a null MediaSource. The live
branch of GetStreamingState then dereferenced it unconditionally, throwing a
NullReferenceException and returning HTTP 500 for every poll until the client
re-opens the stream. Guard against the null MediaSource and throw
ResourceNotFoundException so the request returns 404 instead of crashing.
Fixes#17009
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
zachhide
8ffb54603a