avformat/mxfdec: only probe max run in

Suggested-by: Tomas Härdin <tjoppen@acc.umu.se>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mxfdec.c

@@ -4126,7 +4126,7 @@ static int mxf_read_close(AVFormatContext *s)
 
 static int mxf_probe(const AVProbeData *p) {
     const uint8_t *bufp = p->buf;
-    const uint8_t *end = p->buf + p->buf_size;
+    const uint8_t *end = p->buf + FFMIN(p->buf_size, RUN_IN_MAX + 1 + sizeof(mxf_header_partition_pack_key));
 
     if (p->buf_size < sizeof(mxf_header_partition_pack_key))
         return 0;