Mac/XCB/Windows: Fix initial setting of window icons.

Setting an icon on a QWindow before creating the platform
window did not have any effect.

Task-number: QTBUG-31961
Change-Id: I8e58a3b239c8bc69af58f765e7826337463d2201
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -235,6 +235,8 @@ QCocoaWindow::QCocoaWindow(QWindow *tlw)
     setGeometry(tlw->geometry());
     recreateWindow(parent());
     tlw->setGeometry(geometry());
+    if (tlw->isTopLevel())
+        setWindowIcon(tlw->icon());
     m_inConstructor = false;
 }
 

src/plugins/platforms/windows/qwindowswindow.cpp

@@ -837,6 +837,8 @@ QWindowsWindow::QWindowsWindow(QWindow *aWindow, const WindowData &data) :
     const qreal opacity = qt_window_private(aWindow)->opacity;
     if (!qFuzzyCompare(opacity, qreal(1.0)))
         setOpacity(opacity);
+    if (aWindow->isTopLevel())
+        setWindowIcon(aWindow->icon());
     clearFlag(WithinCreate);
 }
 

src/plugins/platforms/xcb/qxcbwindow.cpp

@@ -458,6 +458,8 @@ void QXcbWindow::create()
     const qreal opacity = qt_window_private(window())->opacity;
     if (!qFuzzyCompare(opacity, qreal(1.0)))
         setOpacity(opacity);
+    if (window()->isTopLevel())
+        setWindowIcon(window()->icon());
 }
 
 QXcbWindow::~QXcbWindow()