app: [Windows] don't draw after WM_DESTROY destroyed the window

There may be a window of time from WM_DESTROY is received to the WM_QUIT
message is delivered by PostQuitMessage. If so, we must not call w.draw.

Fixes: https://todo.sr.ht/~eliasnaur/gio/603
Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/os_windows.go

@@ -558,8 +558,7 @@ func (w *window) runLoop() {
 	msg := new(windows.Msg)
 loop:
 	for {
-		anim := w.animating
-		if anim && !windows.PeekMessage(msg, 0, 0, 0, windows.PM_NOREMOVE) {
+		if w.hwnd != 0 && w.animating && !windows.PeekMessage(msg, 0, 0, 0, windows.PM_NOREMOVE) {
 			w.draw(false)
 			continue
 		}