avformat/aiffdec: AIFF fix in case of ANNO

Apple's AIFF protocol clearly states that each chucnk which is odd sized a padding should be added.
In the old version of aiffdec adding of padding was done in `get_meta`. And in case of unknown chunk name it was done in defalut case.
The new version has deleted the padding in default case and added padding adding after the switch.
But the new version didn't removed the padding adding in the `get_meta` function so in some cases padding was added twice which leaded to a bug.

Fixes: sample.aiff
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/aiffdec.c

@@ -81,11 +81,10 @@ static void get_meta(AVFormatContext *s, const char *key, int size)
             av_free(str);
             return;
         }
-        size += (size&1)-res;
+        size -= res;
         str[res] = 0;
         av_dict_set(&s->metadata, key, str, AV_DICT_DONT_STRDUP_VAL);
-    }else
-        size+= size&1;
+    }
 
     avio_skip(s->pb, size);
 }