[autotests/wayland] Try to make PointerInputTest::testMouseActionActiveWindow more robust

It's currently failing on build.kde.org. I'm not able to reproduce the
failure localy so I can only interpret the failure. The failure looks
like a window is still present in the next executed test case thus
breaking the positioning.

This change ensures that the window is properly gone before going into
the next test case.

autotests/wayland/pointer_input.cpp

@@ -745,6 +745,8 @@ void PointerInputTest::testMouseActionActiveWindow()
     QVERIFY(clientAddedSpy.wait());
     AbstractClient *window1 = workspace()->activeClient();
     QVERIFY(window1);
+    QSignalSpy window1DestroyedSpy(window1, &QObject::destroyed);
+    QVERIFY(window1DestroyedSpy.isValid());
     Surface *surface2 = m_compositor->createSurface(m_compositor);
     QVERIFY(surface2);
     ShellSurface *shellSurface2 = m_shell->createSurface(surface2, surface2);
@@ -754,6 +756,8 @@ void PointerInputTest::testMouseActionActiveWindow()
     AbstractClient *window2 = workspace()->activeClient();
     QVERIFY(window2);
     QVERIFY(window1 != window2);
+    QSignalSpy window2DestroyedSpy(window2, &QObject::destroyed);
+    QVERIFY(window2DestroyedSpy.isValid());
     QCOMPARE(workspace()->topClientOnDesktop(1, -1), window2);
     // geometry of the two windows should be overlapping
     QVERIFY(window1->geometry().intersects(window2->geometry()));
@@ -786,6 +790,11 @@ void PointerInputTest::testMouseActionActiveWindow()
 
     // release again
     kwinApp()->platform()->pointerButtonReleased(button, timestamp++);
+
+    delete surface1;
+    QVERIFY(window1DestroyedSpy.wait());
+    delete surface2;
+    QVERIFY(window2DestroyedSpy.wait());
 }
 
 void PointerInputTest::testCursorImage()