avformat/demux: Remove redundant prevention against infinite loop

This piece of code has been added as FFmpeg's answer to
infinite loops in try_decode_frame() in commit
6072a19b4f. There is no loop
around try_decode_frame() any more, so this code can be removed.

This code is only triggered in case a) the codec parameter could
not be determined, b) the decode delay could not be guessed or
c) no packet was ever encountered and the encoder has the
AV_CODEC_CAP_CHANNEL_CONF. In these cases the new code will
no longer emit a "decoding for stream %d failed" message, which is
prima facie false. In case a) an additional "Could not find codec
parameters" message is (and will be) emitted. No warning will be
emitted any more in case b) (this happens e.g. with some
h264-conformance FATE-files).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/demux.c

@@ -2054,9 +2054,6 @@ static int try_decode_frame(AVFormatContext *s, AVStream *st,
         }
     }
 
-    if (!pkt.data && !got_picture)
-        ret = -1;
-
 fail:
     if (do_skip_frame) {
         avctx->skip_frame = skip_frame;