Fix a __warn_memset_zero_len gcc-4.4 warning.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@20521 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/alsdec.c

@@ -670,6 +670,7 @@ static void zero_remaining(unsigned int b, unsigned int b_max,
     while (b < b_max)
         count += div_blocks[b];
 
+    if (count)
     memset(buf, 0, sizeof(*buf) * count);
 }