add sanity check for language checks ;)

Author: Fabian Pechstein

src/QuickTranslateBundle/Resources/public/js/utilities/isDeeplLanguage.js

@@ -8,6 +8,9 @@
  */
 
 function isDeeplLanguage(lang) {
+    if (!lang) {
+        return false;
+    }
 
     lang = lang.split("_")[0];
 
@@ -25,7 +28,5 @@ function isDeeplLanguage(lang) {
         "zh"
     ];
 
-
-
     return deeplLanguages.includes(lang);
 }