Pass WM_SYSKEYDOWN and WM_SYSKEYUP messages to DefWindowProc after processing them so Windows can still use them for their intended purposes, e.g. ALT+F4
Allowing window-level signal to catch and prevent normal behavior of WM_SYSKEYDOWN and WM_SYSKEYUP messages by setting event to handled
Merge pull request #380 from nselikoff/alt-f4-fix

Allow Windows to process system keystroke messages