avformat/aacdec: Fix leak in adts_aac_read_packet()

Fixes: chromium-773637/clusterfuzz-testcase-minimized-6418078673141760

Found-by: ossfuzz/chromium
Reviewed-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 2779d33ed9)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/aacdec.c

@@ -139,7 +139,11 @@ static int adts_aac_read_packet(AVFormatContext *s, AVPacket *pkt)
         return AVERROR_INVALIDDATA;
     }
 
-    return av_append_packet(s->pb, pkt, fsize - ADTS_HEADER_SIZE);
+    ret = av_append_packet(s->pb, pkt, fsize - ADTS_HEADER_SIZE);
+    if (ret < 0)
+        av_packet_unref(pkt);
+
+    return ret;
 }
 
 AVInputFormat ff_aac_demuxer = {