avformat/segafilm: check 2nd tag

Fixes probetest failure
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/segafilm.c

@@ -69,6 +69,9 @@ static int film_probe(AVProbeData *p)
     if (AV_RB32(&p->buf[0]) != FILM_TAG)
         return 0;
 
+    if (AV_RB32(&p->buf[16]) != FDSC_TAG)
+        return 0;
+
     return AVPROBE_SCORE_MAX;
 }