avformat/mov: Fix memleak

When the mov/mp4 demuxer encounters an error during decrypting a packet,
it returns the error, yet doesn't free the packet, so that the packet
leaks. This has been fixed in this commit.

Fixes the memleaks from ticket #8150.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 34bd293b01)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/mov.c

@@ -7832,8 +7832,10 @@ static int mov_read_packet(AVFormatContext *s, AVPacket *pkt)
         aax_filter(pkt->data, pkt->size, mov);
 
     ret = cenc_filter(mov, st, sc, pkt, current_index);
-    if (ret < 0)
+    if (ret < 0) {
+        av_packet_unref(pkt);
         return ret;
+    }
 
     return 0;
 }