Make sure if we are using a theme, its module is added as a valid domain where...

Make sure if we are using a theme, its module is added as a valid domain where we can look for translations.

lib/SimpleSAML/XHTML/Template.php

@@ -178,11 +178,13 @@ class SimpleSAML_XHTML_Template
             return false;
         }
 
-
         // load extra i18n domains
         if ($this->module) {
             $this->localization->addModuleDomain($this->module);
         }
+        if ($this->theme['module'] !== null && $this->theme['module'] !== $this->module) {
+            $this->localization->addModuleDomain($this->theme['module']);
+        }
 
         $options = array(
             'cache' => $cache,