compositor_wayland: don't commit cursor changes if the layer wasn't actually enabled

The drm backend doesn't handle changes that do this well, as it requests a pageflip event and the
kernel can't give us a pageflip event for an already-disabled plane.

BUG: 495843

src/compositor_wayland.cpp

@@ -537,13 +537,16 @@ void WaylandCompositor::addOutput(Output *output)
             outputLayer->setEnabled(true);
             return output->updateCursorLayer();
         };
+        const bool wasHardwareCursor = outputLayer && outputLayer->isEnabled();
         if (renderHardwareCursor()) {
             cursorLayer->setVisible(false);
             return true;
         } else {
-            if (outputLayer && outputLayer->isEnabled()) {
+            if (outputLayer) {
                 outputLayer->setEnabled(false);
-                output->updateCursorLayer();
+                if (wasHardwareCursor) {
+                    output->updateCursorLayer();
+                }
             }
             cursorLayer->setVisible(cursor->isOnOutput(output));
             cursorLayer->setGeometry(outputLocalRect);