Return an empty array if there are no languages in territory

Only JavaScript is modified here. The corresponding PHP function
is unchanged to preserve consistency with other PHP functions.

Corresponding pull request in jquery.uls:
https://github.com/wikimedia/jquery.uls/pull/370

Downstream bug:
https://phabricator.wikimedia.org/T265158

src/index.js

@@ -281,7 +281,7 @@ function getDir( language ) {
  * @return {string[]} list of language codes
  */
 function getLanguagesInTerritory( territory ) {
-	return languageData.territories[ territory ];
+	return languageData.territories[ territory ] || [];
 }
 
 /**