lib-storage: Fail mailbox list iteration early if it fails to get INB…

…OX flags

The resulting INBOX reply could be wrong in that case.

Also with imapc if the remote server is down, this causes two connection
errors instead of just one.

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

@@ -707,17 +707,19 @@ patterns_match_inbox(struct mail_namespace *namespaces,
 	return imap_match(glob, "INBOX") == IMAP_MATCH_YES;
 }
 
-static void inbox_info_init(struct ns_list_iterate_context *ctx,
-			    struct mail_namespace *namespaces)
+static int inbox_info_init(struct ns_list_iterate_context *ctx,
+			   struct mail_namespace *namespaces)
 {
 	enum mailbox_info_flags flags;
+	int ret;
 
 	ctx->inbox_info.vname = "INBOX";
 	ctx->inbox_info.ns = mail_namespace_find_inbox(namespaces);
 	i_assert(ctx->inbox_info.ns != NULL);
 
-	if (mailbox_list_mailbox(ctx->inbox_info.ns->list, "INBOX", &flags) > 0)
+	if ((ret = mailbox_list_mailbox(ctx->inbox_info.ns->list, "INBOX", &flags)) > 0)
 		ctx->inbox_info.flags = flags;
+	return ret;
 }
 
 struct mailbox_list_iterate_context *
@@ -754,7 +756,10 @@ mailbox_list_iter_init_namespaces(struct mail_namespace *namespaces,
 		   else called INBOX (e.g. namespace prefix) we can show it
 		   immediately with the proper flags. */
 		ctx->inbox_list = TRUE;
-		inbox_info_init(ctx, namespaces);
+		if (inbox_info_init(ctx, namespaces) < 0) {
+			pool_unref(&pool);
+			return &mailbox_list_iter_failed;
+		}
 	}
 
 	if ((flags & MAILBOX_LIST_ITER_STAR_WITHIN_NS) != 0) {