ICore: Fix possible crash in raiseWindow()

Don't call else branch with nullptr when window is nullptr.

Amends 79be19a8a0

Change-Id: I4c1ee3783d36374cbc6ad9555328b5737f2ce348
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/coreplugin/icore.cpp

@@ -720,7 +720,9 @@ void ICore::raiseWindow(QWidget *widget)
     if (!widget)
         return;
     QWidget *window = widget->window();
-    if (window && window == m_mainwindow) {
+    if (!window)
+        return;
+    if (window == m_mainwindow) {
         m_mainwindow->raiseWindow();
     } else {
         window->raise();