avformat/utils: Fix memleaks II

Up until now, avformat_find_stream_info had a potential for memleaks:
When everything was fine, it read packets and (depending upon whether
AVFMT_FLAG_NOBUFFER was set) put them in a packet list or unreferenced
them when they were no longer needed. But upon failure, said packets
would leak if they were not already on the packet list. This patch fixes
this.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/utils.c

@@ -3812,7 +3812,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
                                      &ic->internal->packet_buffer_end,
                                      &pkt1, 0);
             if (ret < 0)
-                goto find_stream_info_err;
+                goto unref_then_goto_end;
 
             pkt = &ic->internal->packet_buffer_end->pkt;
         } else {
@@ -3827,7 +3827,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
         if (!st->internal->avctx_inited) {
             ret = avcodec_parameters_to_context(avctx, st->codecpar);
             if (ret < 0)
-                goto find_stream_info_err;
+                goto unref_then_goto_end;
             st->internal->avctx_inited = 1;
         }
 
@@ -3915,7 +3915,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
         if (!st->internal->avctx->extradata) {
             ret = extract_extradata(st, pkt);
             if (ret < 0)
-                goto find_stream_info_err;
+                goto unref_then_goto_end;
         }
 
         /* If still no information, we try to open the codec and to
@@ -4191,6 +4191,10 @@ find_stream_info_err:
         av_log(ic, AV_LOG_DEBUG, "After avformat_find_stream_info() pos: %"PRId64" bytes read:%"PRId64" seeks:%d frames:%d\n",
                avio_tell(ic->pb), ic->pb->bytes_read, ic->pb->seek_count, count);
     return ret;
+
+unref_then_goto_end:
+    av_packet_unref(&pkt1);
+    goto find_stream_info_err;
 }
 
 AVProgram *av_find_program_from_stream(AVFormatContext *ic, AVProgram *last, int s)