Merge pull request #6 from novnc/master

Avoid exception when cursor was removed from DOM already

core/util/cursor.js

@@ -69,8 +69,10 @@ export default class Cursor {
             this._target.removeEventListener('mousemove', this._eventHandlers.mousemove, options);
             this._target.removeEventListener('mouseup', this._eventHandlers.mouseup, options);
 
+            if (document.contains(this._canvas)) {
                 document.body.removeChild(this._canvas);
             }
+        }
 
         this._target = null;
     }