[gnome-shell] Magnifier: fix a warning when calling setActive() with the same value

[Giovanni Campagna <gcampagna src gnome org>]

commit 3b0197620fcd98de9be79f5245ca1079033563ee
Author: Giovanni Campagna <gcampagna src gnome org>
Date:   Thu Feb 13 15:11:07 2014 +0100

    Magnifier: fix a warning when calling setActive() with the same value
    
    We must not call enable/disable_unredirect if we didn't change the
    active value, otherwise mutter gets confused and emits warnings.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=724293

 js/ui/magnifier.js |   17 ++++++++++-------
 1 files changed, 10 insertions(+), 7 deletions(-)
---
diff --git a/js/ui/magnifier.js b/js/ui/magnifier.js
index 96c12b2..81e3553 100644
--- a/js/ui/magnifier.js
+++ b/js/ui/magnifier.js
@@ -105,17 +105,20 @@ const Magnifier = new Lang.Class({
      * @activate:   Boolean to activate or de-activate the magnifier.
      */
     setActive: function(activate) {
+        let isActive = this.isActive();
+
         this._zoomRegions.forEach (function(zoomRegion, index, array) {
             zoomRegion.setActive(activate);
         });
 
-        if (activate) {
-            Meta.disable_unredirect_for_screen(global.screen);
-            this.startTrackingMouse();
-        }
-        else {
-            Meta.enable_unredirect_for_screen(global.screen);
-            this.stopTrackingMouse();
+        if (isActive != activate) {
+            if (activate) {
+                Meta.disable_unredirect_for_screen(global.screen);
+                this.startTrackingMouse();
+            } else {
+                Meta.enable_unredirect_for_screen(global.screen);
+                this.stopTrackingMouse();
+            }
         }
 
         // Make sure system mouse pointer is shown when all zoom regions are