Revert "lavd video: don't print false positive errs"

This reverts commit d4be2d97b5.

The fix was not correct, because it just hided the root of the problem -
the av_parser_parse2 needs final call with buf_size == 0 to flush last
frame. Otherwise it will remain in the queue, effectivelly adding a
delay by one frame, because the particular frame will get flushed when
processing next frame.

See also:
<https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/decode_video.c>

src/video_decompress/libavcodec.c

@@ -996,7 +996,6 @@ decode_frame(struct state_libavcodec_decompress *s, unsigned char *src,
                         }
                 }
                 if (s->pkt->size == 0) {
-                        ret = 0;
                         break;
                 }
                 src += ret;