avformat/mxfdec: do not allow more partitions than INT_MAX/2

Some math (e.g: partition binary search) overflows if we have that many
parititions.
Signed-off-by: Marton Balint <cus@passwd.hu>

libavformat/mxfdec.c

@@ -565,6 +565,9 @@ static int mxf_read_partition_pack(void *arg, AVIOContext *pb, int tag, int size
     uint64_t footer_partition;
     uint32_t nb_essence_containers;
 
+    if (mxf->partitions_count >= INT_MAX / 2)
+        return AVERROR_INVALIDDATA;
+
     tmp_part = av_realloc_array(mxf->partitions, mxf->partitions_count + 1, sizeof(*mxf->partitions));
     if (!tmp_part)
         return AVERROR(ENOMEM);