Make Window::closeWindow() noop if the window is already closed

The surface handle can be dropped by that time. Also, there is no point
to ask the client to close the window again if it's already closed.

src/internalwindow.cpp

@@ -172,7 +172,7 @@ QString InternalWindow::windowRole() const
 
 void InternalWindow::closeWindow()
 {
-    if (m_handle) {
+    if (!isDeleted()) {
         m_handle->hide();
     }
 }

src/layershellv1window.cpp

@@ -211,7 +211,9 @@ void LayerShellV1Window::destroyWindow()
 
 void LayerShellV1Window::closeWindow()
 {
-    m_shellSurface->sendClosed();
+    if (!isDeleted()) {
+        m_shellSurface->sendClosed();
+    }
 }
 
 Layer LayerShellV1Window::belongsToLayer() const

src/x11window.cpp

@@ -2031,6 +2031,9 @@ bool X11Window::isCloseable() const
  */
 void X11Window::closeWindow()
 {
+    if (isDeleted()) {
+        return;
+    }
     if (!isCloseable()) {
         return;
     }

src/xdgshellwindow.cpp

@@ -668,6 +668,9 @@ void XdgToplevelWindow::applyWindowRules()
 
 void XdgToplevelWindow::closeWindow()
 {
+    if (isDeleted()) {
+        return;
+    }
     if (isCloseable()) {
         sendPing(PingReason::CloseWindow);
         m_shellSurface->sendClose();