avformat/mxfdec: Free all types for both Descriptors

Fixes: memleak
Fixes: 26352/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5201158714687488

Suggested-by: Tomas Härdin <tjoppen@acc.umu.se>
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 88519be8db)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mxfdec.c

@@ -330,9 +330,8 @@ static void mxf_free_metadataset(MXFMetadataSet **ctx, int freectx)
     MXFIndexTableSegment *seg;
     switch ((*ctx)->type) {
     case Descriptor:
-        av_freep(&((MXFDescriptor *)*ctx)->extradata);
-        break;
     case MultipleDescriptor:
+        av_freep(&((MXFDescriptor *)*ctx)->extradata);
         av_freep(&((MXFDescriptor *)*ctx)->sub_descriptors_refs);
         break;
     case Sequence: