x11: Properly unredirect windows if compositing is not possible

Before attempting to create scenes, kwin will redirect windows but if
the opengl scene can't be created, it won't unredirect windows, which
seems to cause issues on aarch64.

BUG: 443953

src/composite.cpp

@@ -251,6 +251,10 @@ bool Compositor::setupStart()
         delete m_scene;
         m_scene = nullptr;
 
+        if (auto *con = kwinApp()->x11Connection()) {
+            xcb_composite_unredirect_subwindows(con, kwinApp()->x11RootWindow(),
+                                                XCB_COMPOSITE_REDIRECT_MANUAL);
+        }
         if (m_selectionOwner) {
             m_selectionOwner->setOwning(false);
             m_selectionOwner->release();