macOS: Ensure NSWindow delegate is released in sync with its NSWindow

Releasing it in [QNSWindow closeAndRelease] is wrong, as we only call
that method from a few call sites, and can easily end up with a normal
dealloc by means of e.g. the [m_nsWindow release] in ~QCocoaWindow.

This still leaves Xcode thinking we have a single leaking delegate
per active NSWindow, as it apparently doesn't realize we're calling
release manually. This needs to be investigated further.

Task-number: QTBUG-65693
Change-Id: I9105602274d8532465e5108aba2b05bf253268e9
Reviewed-by: Andy Shaw <andy.shaw@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

src/plugins/platforms/cocoa/qnswindow.mm

@@ -239,10 +239,6 @@ static bool isMouseEvent(NSEvent *ev)
 - (void)closeAndRelease
 {
     qCDebug(lcQpaWindow) << "closeAndRelease" << self;
-
-    [self.delegate release];
-    self.delegate = nil;
-
     [self close];
     [self release];
 }
@@ -252,6 +248,9 @@ static bool isMouseEvent(NSEvent *ev)
 - (void)dealloc
 {
     qCDebug(lcQpaWindow) << "dealloc" << self;
+    [self.delegate release];
+    self.delegate = nil;
+
     qt_objcDynamicSuper();
 }
 #pragma clang diagnostic pop