[Fuchsia] Update audio buffering state at EOS.

Previously FuchsiaAudioRenderer was stopping at EOS without updating
buffering state to HAVE_ENOUGH. This means that when stream is seeked to
the end of file playback never resumes. Fixed it to update buffering
state as soon as EOS is reached.

Bug: 1162503
Change-Id: I57d6a08469830c069a13252c4767f3b7f57ed24a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2606034
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Auto-Submit: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840224}

media/fuchsia/audio/fuchsia_audio_renderer.cc

@@ -523,6 +523,12 @@ void FuchsiaAudioRenderer::OnDemuxerStreamReadDone(
       SetPlaybackState(PlaybackState::kEndOfStream);
     }
     stream_sink_->EndOfStream();
+
+    // No more data is going to be biffered. Update buffering state to ensure
+    // RendererImpl starts playback in case it was waiting for buffering to
+    // finish.
+    SetBufferState(BUFFERING_HAVE_ENOUGH);
+
     return;
   }