Mouse: Fix case when no screen container is given

src/browser/mouse.js

@@ -209,10 +209,13 @@ function MouseAdapter(bus, screen_container)
 
         mouse.bus.send("mouse-delta", [delta_x, delta_y]);
 
-        let absolute_x = e.pageX - screen_container.offsetLeft;
-        let absolute_y = e.pageY - screen_container.offsetTop;
-        mouse.bus.send("mouse-absolute", [
-            absolute_x, absolute_y, screen_container.offsetWidth, screen_container.offsetHeight]);
+        if(screen_container)
+        {
+            let absolute_x = e.pageX - screen_container.offsetLeft;
+            let absolute_y = e.pageY - screen_container.offsetTop;
+            mouse.bus.send("mouse-absolute", [
+                absolute_x, absolute_y, screen_container.offsetWidth, screen_container.offsetHeight]);
+        }
     }
 
     function mousedown_handler(e)