rawdec: fix mjpeg probing buffer size check

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 4c6beaed92)

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/rawdec.c

@@ -189,7 +189,7 @@ static int mjpeg_probe(AVProbeData *p)
         static const char ct_jpeg[] = "\r\nContent-Type: image/jpeg\r\n";
         int i;
 
-        for (i=0; i<FFMIN(p->buf_size - sizeof(ct_jpeg), 100); i++)
+        for (i=0; i<FFMIN(p->buf_size - (int)sizeof(ct_jpeg), 100); i++)
             if (!memcmp(p->buf + i, ct_jpeg, sizeof(ct_jpeg) - 1))
                 return AVPROBE_SCORE_EXTENSION;