id3: allow 4 MB RIFF/AIFF tags

Allow RIFF/AIFF ID3 tags up to 4 MB (old limit was 256 kB).  This
might still be too small for some users, and when somebody complains,
we might do something more clever (like streaming the data into
libid3tag?).

src/tag_id3.c

@@ -481,7 +481,7 @@ tag_id3_riff_aiff_load(FILE *file)
 	if (size == 0)
 		return NULL;
 
-	if (size > 256 * 1024)
+	if (size > 4 * 1024 * 1024)
 		/* too large, don't allocate so much memory */
 		return NULL;