Fix crash when accessing ShellClient::iconGeometry for a not mapped window

It uses windowManagementInterface which is null until the window
is mapped. A not mapped window obviously has an invalid iconGeometry.

autotests/wayland/start_test.cpp

@@ -127,6 +127,10 @@ void StartTest::testCreateWindow()
     // but still not yet in workspace
     QVERIFY(workspace()->allClientList().isEmpty());
 
+    // icon geometry accesses windowManagementInterface which only exists after window became visible
+    // verify that accessing doesnt't crash
+    QVERIFY(waylandServer()->clients().first()->iconGeometry().isNull());
+
     // let's render
     QImage img(QSize(100, 50), QImage::Format_ARGB32);
     img.fill(Qt::blue);

shell_client.cpp

@@ -473,6 +473,11 @@ bool ShellClient::isMinimizable() const
 
 QRect ShellClient::iconGeometry() const
 {
+    if (!windowManagementInterface()) {
+        // window management interface is only available if the surface is mapped
+        return QRect();
+    }
+
     int minDistance = INT_MAX;
     ShellClient *candidatePanel = nullptr;
     QRect candidateGeom;