Multi touch fails if no normal touch have happend before

Multi touch fails with:
NOT_SUPPORTED_ERR: DOM Exception 9: The implementation did not support the requested type of object or operation.

because of pos being ```{x: NaN, y: NaN}```  at
```var p = layer.hitCanvas.context.getImageData(Math.round(pos.x), Math.round(pos.y), 1, 1).data;````
in ```getIntersection(pos)````

Setting stage defaults to the following solves that problem.

```
   /**
     * set defaults
     */
    _setStageDefaultProperties: function() {
        this.nodeType = 'Stage';
        this.dblClickWindow = 400;
        this.targetShape = null;
        this.mousePos = {
            x: 0,
            y: 0
        };
        this.clickStart = false;
        this.touchPos = {
            x: 0,
            y: 0
        };
        this.tapStart = false;

        /*
         * ids and names hash needs to be stored at the stage level to prevent
         * id and name collisions between multiple stages in the document
         */
        this.ids = {};
        this.names = {};
    }
```