avformat/mxfdec: Check for duplicate mxf_read_index_entry_array()

Fixes: memleak
Fixes: 41596/clusterfuzz-testcase-minimized-ffmpeg_dem_MXF_fuzzer-6439060204290048

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Tomas Härdin <tjoppen@acc.umu.se>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mxfdec.c

@@ -1111,6 +1111,9 @@ static int mxf_read_index_entry_array(AVIOContext *pb, MXFIndexTableSegment *seg
 {
     int i, length;
 
+    if (segment->temporal_offset_entries)
+        return AVERROR_INVALIDDATA;
+
     segment->nb_index_entries = avio_rb32(pb);
 
     length = avio_rb32(pb);