don't use textured mousecursor unless required

REVIEW: 107424
BUG: 276391
FIXED-IN: 4.10

effects/zoom/zoom.cpp

@@ -154,6 +154,8 @@ void ZoomEffect::showCursor()
 
 void ZoomEffect::hideCursor()
 {
+    if (mouseTracking == MouseTrackingProportional && mousePointer == MousePointerKeep)
+        return; // don't replace the actual cursor by a static image for no reason.
     if (!isMouseHidden) {
         // try to load the cursor-theme into a OpenGL texture and if successful then hide the mouse-pointer
         recreateTexture();