[FIX] web_editor: show XML editor error if rejection value

Override in enterprise web_studio of _saveView on error never rejected
promises. But now it does so the XML editor interface is not blocked
after error.

But we were already showing the correct error in web_studio use case, so
we don't want another one and this change allow that by only showing an
error if we received rejection value.

opw-2460081

closes odoo/odoo#68569

X-original-commit: 43184af875f3eb52586348b383627cb0140484f5
Related: odoo/enterprise#17395
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>

addons/web_editor/static/src/js/common/ace.js

@@ -629,6 +629,10 @@ var ViewEditor = Widget.extend({
 
         var self = this;
         return Promise.all(defs).guardedCatch(function (results) {
+            // some overrides handle errors themselves
+            if (results === undefined) {
+                return;
+            }
             var error = results[1];
             Dialog.alert(self, '', {
                 title: _t("Server error"),