improve probe and give it the max score

Originally committed as revision 7667 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/flvdec.c

@@ -34,8 +34,8 @@ static int flv_probe(AVProbeData *p)
     if (p->buf_size < 6)
         return 0;
     d = p->buf;
-    if (d[0] == 'F' && d[1] == 'L' && d[2] == 'V') {
-        return 50;
+    if (d[0] == 'F' && d[1] == 'L' && d[2] == 'V' && d[3] < 5 && d[5]==0) {
+        return AVPROBE_SCORE_MAX;
     }
     return 0;
 }