Fixes autoEnableDesktopSharing option.

app.js

     var isUIReady = APP.UI.start();
     if (isUIReady) {
         APP.conference.init({roomName: buildRoomName()}).then(function () {
+            // init desktop before UI, in order to make sure
+            // autoEnableDesktopSharing works
+            APP.desktopsharing.init(JitsiMeetJS.isDesktopSharingEnabled());
+
             APP.UI.initConference();
 
             APP.UI.addListener(UIEvents.LANG_CHANGED, function (language) {
                 APP.settings.setLanguage(language);
             });
 
-            APP.desktopsharing.init(JitsiMeetJS.isDesktopSharingEnabled());
             APP.keyboardshortcut.init();
         }).catch(function (err) {
             console.error(err);