Spin boxes use value of "-0"

1. Open a qml file in Design mode.
2. Select an item.
3. In Geometry editor, enter "-0" into all spin boxes.
   The Designer accepts this.
4. Go to Edit mode.
   Values of "0" have been written to the file.
5. Change the file.
6. Go back to Design mode.
   In "X" and "Y" spin boxes, you'll still see "-0".

A value of "-0" should never be shown or used. It should be changed to "0" immediately.