Enable skipping loop filter and allow non spec compliant speedup tricks.
to enable, create new boolean pref "media.ffmpeg.skip_loop_filter" and set it to true.
According to FFmpeg documentation, the out parameter is "set to size of parsed buffer or zero if not yet finished." however this is only the case if no error occurred; otherwise it is left untouched. We want the invalid content to generate a decoding error, so we set size to inputSize to ensure decoding failed later.
