lib-storage: Fix mailbox delete to not delete childrens' INDEX or CON…

…TROL dirs

If mail_location had separate INDEX and/or CONTROL set, deleting a mailbox
with children caused the childrens' index and/or control directories to be
deleted (but the mail/ALT directories weren't).

I'm not sure why the _FLAG_MAILBOX_FILES was treated as a special case
earlier. It shouldn't make a difference.

src/lib-storage/list/mailbox-list-delete.c

@@ -296,8 +296,10 @@ static int mailbox_list_try_delete(struct mailbox_list *list, const char *name,
 	    strcmp(path, mailbox_path) == 0)
 		return 0;
 
-	if (*list->set.maildir_name == '\0' &&
-	    (list->flags & MAILBOX_LIST_FLAG_MAILBOX_FILES) == 0) {
+	/* Note that only ALT currently uses maildir_name in paths.
+	   INDEX and CONTROL don't. */
+	if (type != MAILBOX_LIST_PATH_TYPE_ALT_MAILBOX ||
+	    *list->set.maildir_name == '\0') {
 		/* this directory may contain also child mailboxes' data.
 		   we don't want to delete that. */
 		bool rmdir_path = *list->set.maildir_name != '\0';