The target editor was only create the cursor shape if the mouse was moved, but the cursor shape was set to None on click (when the region was added.) This made is to that if a  user clicked to add a shape, didn't move the mouse, and clicked again the subsequent shapes would not actually be created and None would be added to the region list. This culminated in a Tcl exception when trying to get the coords of None. This finishes closing #57.