VisibleLayer: fix a bug in which the onVisibleChanged callback was ge…

…tting fired before the state changed when using _visibleTiedToOpen==true, as in an ElevationLayer

src/osgEarth/VisibleLayer.cpp

@@ -215,15 +215,15 @@ VisibleLayer::setVisible(bool value)
 
         updateNodeMasks();
 
-        onVisibleChanged.fire(this);
-
         if (_visibleTiedToOpen)
         {
             if (value && !isOpen())
                 open();
             else if (!value && isOpen())
                 close();
         }
+
+        onVisibleChanged.fire(this);
     }
 }