Fixes a potential AV when ActiveWidget is freed
Fixes a potential AV when ActiveWidget is freed

If the ActiveWidget was freed, the parent never got notified. If focus was
then changed, the parent tried to call ActiveWidget.HandleFocusKill, causing
an access violation.

The toolkit now correctly sets ActiveWidget to nil if it was freed, and as
a extra failsafe, wraps the HandleFocusKill call in a try..except block.

wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI