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/idcin.c

@@ -104,10 +104,6 @@ static int idcin_probe(AVProbeData *p)
      * audio channels: 0 for no audio, or 1 or 2
      */
 
-    /* cannot proceed without 20 bytes */
-    if (p->buf_size < 20)
-        return 0;
-
     /* check the video width */
     number = AV_RL32(&p->buf[0]);
     if ((number == 0) || (number > 1024))