app: delay Window.Close until after event processing

The fix for #340, b2a99fddca, deferred
all driver functions until after event processing. Deferring functions
breaks Window.Run which expects to complete during event processing.
This change is an alternative, more targeted fix, namely deferring just
Window.Close until after event processing.

A follow-up will revert the previous fix.

References: https://todo.sr.ht/~eliasnaur/gio/340
Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/window.go

@@ -54,6 +54,7 @@ type Window struct {
 	out      chan event.Event
 	frames   chan *op.Ops
 	frameAck chan struct{}
+	closing  bool
 	// dead is closed when the window is destroyed.
 	dead chan struct{}
 
@@ -326,7 +327,7 @@ func (w *Window) SetCursorName(name pointer.CursorName) {
 // all others are stubbed.
 func (w *Window) Close() {
 	w.driverDefer(func(d driver) {
-		d.Close()
+		w.closing = true
 	})
 }
 
@@ -429,6 +430,10 @@ func (c *callbacks) Event(e event.Event) {
 	}
 	c.w.defers = c.w.defers[:0]
 	c.w.updateState(c.d)
+	if c.w.closing {
+		c.w.closing = false
+		c.d.Close()
+	}
 }
 
 // SemanticRoot returns the ID of the semantic root.