Sometimes the Windows Media Foundation MFT video decoder reports that it will
provide memory for output video frames, and the decoder returns success, but it
doesn't output a valid video frame. So change our code to not assume that
output is always valid (to fix a null pointer dereference). We can't reproduce
this locally, so we don't know how to get a best behaviour here, so add
telemetry to figure out whether the decoder will right itself, or whether we
should just give up completely.
--HG--
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