force screen_mode to string type (IE returns a number which is always...

force screen_mode to string type (IE returns a number which is always triggering the default option in the following switch/case block

lib/tpl/dokuwiki/script.js

@@ -12,7 +12,7 @@ var device_classes = 'desktop mobile tablet phone';
 function tpl_dokuwiki_mobile(){
 
     // the z-index in mobile.css is (mis-)used purely for detecting the screen mode here
-    var screen_mode = jQuery('#screen__mode').css('z-index');
+    var screen_mode = jQuery('#screen__mode').css('z-index') + '';
 
     // determine our device pattern
     // TODO: consider moving into dokuwiki core