Bug 1788135 - Fix "Assertion failure: !IsDOMException()" when running…

… with rr r=platform-i18n-reviewers,gregtatum

This only fixes the crash, not the root cause of the error.
See https://bugzilla.mozilla.org/show_bug.cgi?id=1788135#c16

Differential Revision: https://phabricator.services.mozilla.com/D163833

dom/l10n/DOMLocalization.cpp

@@ -347,6 +347,11 @@ already_AddRefed<Promise> DOMLocalization::TranslateElements(
 
     FormatMessagesSync(l10nKeys, l10nMessages, aRv);
 
+    if (NS_WARN_IF(aRv.Failed())) {
+      promise->MaybeRejectWithUndefined();
+      return MaybeWrapPromise(promise);
+    }
+
     bool allTranslated =
         ApplyTranslations(domElements, l10nMessages, aProto, aRv);
     if (NS_WARN_IF(aRv.Failed()) || !allTranslated) {