avformat/utils: unref packet on AVInputFormat.read_packet() failure

Demuxers may have allocated a packet before encountering an error and aborting.

Fixes ticket #8150
Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/utils.c

@@ -854,6 +854,8 @@ int ff_read_packet(AVFormatContext *s, AVPacket *pkt)
         av_init_packet(pkt);
         ret = s->iformat->read_packet(s, pkt);
         if (ret < 0) {
+            av_packet_unref(pkt);
+
             /* Some demuxers return FFERROR_REDO when they consume
                data and discard it (ignored streams, junk, extradata).
                We must re-call the demuxer to get the real packet. */