Make sure script execution doesn't stop by assuming unchecked input is set

These methods aren't designed to return "undefined" or "null".
What they return is not checked. It's assumed to always be an
object (2 of them) or an array (1 of them). This simple patch
does make sure the following code does not fail with TypeErrors.

Bug: 55701
Change-Id: I19f51bbff2209044485b9d7cef4c7654cb5f6425

resources/js/ext.uls.init.js

@@ -140,7 +140,7 @@
 	};
 
 	mw.uls.getAcceptLanguageList = function () {
-		return mw.config.get( 'wgULSAcceptLanguageList' );
+		return mw.config.get( 'wgULSAcceptLanguageList' ) || [];
 	};
 
 	/**