avformat/mxfdec: Check size for shrinking

av_shrink_packet() takes int size, so size must fit in int
Fixes: out of array access
Fixes: 35607/clusterfuzz-testcase-minimized-ffmpeg_dem_MXF_fuzzer-4875541323841536

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

libavformat/mxfdec.c

@@ -622,7 +622,7 @@ static int mxf_decrypt_triplet(AVFormatContext *s, AVPacket *pkt, KLVPacket *klv
         return AVERROR_INVALIDDATA;
     // enc. code
     size = klv_decode_ber_length(pb);
-    if (size < 32 || size - 32 < orig_size)
+    if (size < 32 || size - 32 < orig_size || (int)orig_size != orig_size)
         return AVERROR_INVALIDDATA;
     avio_read(pb, ivec, 16);
     avio_read(pb, tmpbuf, 16);