avformat/jacosubdec: Fix leak on error

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/jacosubdec.c

@@ -199,6 +199,7 @@ static int jacosub_read_header(AVFormatContext *s)
 
             sub = ff_subtitles_queue_insert(&jacosub->q, line, len, merge_line);
             if (!sub) {
+                av_bprint_finalize(&header, NULL);
                 ret = AVERROR(ENOMEM);
                 goto fail;
             }