avformat/ffmetadec: finalize AVBPrint on errors

Fixes: memleak
Fixes: 26450/clusterfuzz-testcase-minimized-ffmpeg_dem_FFMETADATA_fuzzer-6249850443923456

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit a927128617)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/ffmetadec.c

@@ -182,7 +182,7 @@ static int read_header(AVFormatContext *s)
             AVStream *st = avformat_new_stream(s, NULL);
 
             if (!st)
-                return AVERROR(ENOMEM);
+                goto nomem;
 
             st->codecpar->codec_type = AVMEDIA_TYPE_DATA;
             st->codecpar->codec_id   = AV_CODEC_ID_FFMETADATA;
@@ -192,7 +192,7 @@ static int read_header(AVFormatContext *s)
             AVChapter *ch = read_chapter(s);
 
             if (!ch)
-                return AVERROR(ENOMEM);
+                goto nomem;
 
             m = &ch->metadata;
         } else
@@ -208,6 +208,10 @@ static int read_header(AVFormatContext *s)
                                    AV_TIME_BASE_Q);
 
     return 0;
+nomem:
+    av_bprint_finalize(&bp, NULL);
+
+    return AVERROR(ENOMEM);
 }
 
 static int read_packet(AVFormatContext *s, AVPacket *pkt)