allocate 32 extra bytes at the end of the probe buffer and remove most probe buf_size checks

Originally committed as revision 8677 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/avs.c

@@ -47,8 +47,6 @@ static int avs_probe(AVProbeData * p)
 {
     const uint8_t *d;
 
-    if (p->buf_size < 2)
-        return 0;
     d = p->buf;
     if (d[0] == 'w' && d[1] == 'W' && d[2] == 0x10 && d[3] == 0)
         return 50;