Comment 6 for bug 1847532

@Seth, I had first tried to put the tool stack clearance into the dtor for the tool manager, but the problem is it is called explicitly from the EDA_BASE_FRAME dtor. What then happened was if a tool was active (such as the point editor), it would crash because the tool was trying to access the board in Pcbnew, but that board is destroyed in one of the subclasses of EDA_BASE_FRAME, so it was destroyed first. That is why I had to go the more drastic route of putting the stack emptying at the beginning of the frame dtor.