avformat: Dont stop probing before the whole id3 tag is read

When a file appears to start with a id3 tag and appears to
also be something else, then try to increase the probe buffer
size if its below its limit.

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

libavformat/utils.c

@@ -388,6 +388,8 @@ AVInputFormat *av_probe_input_format3(AVProbeData *pd, int is_opened, int *score
         }else if (score == score_max)
             fmt = NULL;
     }
+    if(nodat)
+        score_max = FFMIN(AVPROBE_SCORE_MAX/4-1, score_max);
     *score_ret= score_max;
 
     return fmt;