In `ExternalTextureManager` in seemingly rare cases end of stream is signaled
at the point where a frame is currently pending processing. In that case the
video end of stream signal was lost. If the muxer timeout was enabled this
case would result in throwing an exception, but otherwise the operation would
get stuck
Add code to signal end of stream in `onInputFrameProcessed` as well, so that we
signal end of stream when the pending frame is handled.
Tested by running
`TransformerEndToEndTest.loopingTranscodedVideo_producesExpectedResult` several
times.
PiperOrigin-RevId: 524361069
011fc9d5d3