avformat/smacker: check width/height in probe

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

libavformat/smacker.c

@@ -92,11 +92,14 @@ static const uint8_t smk_pal[64] = {
 
 static int smacker_probe(AVProbeData *p)
 {
-    if(p->buf[0] == 'S' && p->buf[1] == 'M' && p->buf[2] == 'K'
-        && (p->buf[3] == '2' || p->buf[3] == '4'))
-        return AVPROBE_SCORE_MAX;
-    else
+    if (   AV_RL32(p->buf) != MKTAG('S', 'M', 'K', '2')
+        && AV_RL32(p->buf) != MKTAG('S', 'M', 'K', '4'))
         return 0;
+
+    if (AV_RL32(p->buf+4) > 32768U || AV_RL32(p->buf+8) > 32768U)
+        return AVPROBE_SCORE_MAX/4;
+
+    return AVPROBE_SCORE_MAX;
 }
 
 static int smacker_read_header(AVFormatContext *s)