avformat/concatdec: Use FAIL() macro instead of direct return in concat_parse_script()

Fixes: memleak
Fixes: 38893/clusterfuzz-testcase-minimized-ffmpeg_dem_CONCAT_fuzzer-4785231933079552

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/concatdec.c

@@ -627,7 +627,7 @@ static int concat_parse_script(AVFormatContext *avf)
             chapter = avpriv_new_chapter(avf, arg_int[0], AV_TIME_BASE_Q,
                                          arg_int[1], arg_int[2], NULL);
             if (!chapter)
-                return AVERROR(ENOMEM);
+                FAIL(ENOMEM);
             break;
 
         default: