Fix ImageView zoomEnabled bug

Setting zoomEnabled to false while it is already disabled would attempt
to also reset the min/max/level values which can not be reset while
disabled.

Change-Id: I685f69e0694c0acc1b6e41daed91073de8d9a472

doc/api/widgets/ImageView.json

@@ -42,6 +42,7 @@
     "zoomEnabled": {
       "type": "boolean",
       "description": "Enables the pinch-to-zoom gesture on the `ImageView` and makes the properties `zoomLevel`, `minZoomLevel` and `maxZoomLevel` available. Setting `zoomEnabled` to `false` also resets the `zoomLevel`, `minZoomLevel`, `maxZoomLevel` to their respective defaults.",
+      "default": false,
       "platforms": {
         "windows": false
       }

src/tabris/widgets/ImageView.js

@@ -37,14 +37,17 @@ NativeObject.defineProperties(ImageView.prototype, {
   },
   zoomEnabled: {
     type: 'boolean',
+    default: false,
     set(name, value) {
-      if (!value) {
-        this.minZoomLevel = 1;
-        this.maxZoomLevel = 3;
-        this.zoomLevel = 1;
+      if (this.zoomEnabled !== value) {
+        if (!value) {
+          this.minZoomLevel = 1;
+          this.maxZoomLevel = 3;
+          this.zoomLevel = 1;
+        }
+        this._nativeSet(name, value);
+        this._storeProperty(name, value);
       }
-      this._nativeSet(name, value);
-      this._storeProperty(name, value);
     }
   },
   zoomLevel: {

test/tabris/widgets/ImageView.test.js

@@ -83,6 +83,14 @@ describe('ImageView', function() {
         expect(client.calls({op: 'set', id: imageView.cid})[1].properties.zoomLevel).to.equal(1.0);
       });
 
+      it('set false does not reset zoomLevel, minZoomLevel and maxZoomLevel when already disabled', function() {
+        imageView.zoomEnabled = false;
+        client.resetCalls();
+        imageView.zoomEnabled = false;
+
+        expect(client.calls({op: 'set', id: imageView.cid})).to.be.empty;
+      });
+
     });
 
     describe('zoomLevel', function() {