Fix free with uninitialized data in opus_tags_parse().

If the parsing fails before all comments are filled in, we will
 attempt to free any binary metadata at the position one past the
 last comment, which will be uninitialized.
Introduced in commit 0221ca95.

src/info.c

@@ -199,6 +199,7 @@ static int opus_tags_parse_impl(OpusTags *_tags,
       if(_tags->user_comments[ci]==NULL)return OP_EFAULT;
       _tags->comment_lengths[ci]=(int)count;
       _tags->comments=ci+1;
+      _tags->user_comments[ci+1]=NULL;
     }
     _data+=count;
     len-=count;