minLeft is relative to original position and not to screen

I try to set the bounds of the draggable to the screen by setting `minTop` and `minLeft` to `0` and `maxTop` and `maxLeft` to the platform width/height minus the draggable width/height.

All works fine except for `minLeft`. If I set this to 0 the draggable can not be moved left of the original position.
