skins2: slider fix notifyLayout wrongly removed

redefining notifyLayout is mandatory for sliders, because the default
notifyLayout based on position doesn't work well for this complicated control.
This function is called when visibility is turned on or off.

modules/gui/skins2/controls/ctrl_slider.cpp

@@ -153,6 +153,24 @@ void CtrlSliderCursor::onResize()
 }
 
 
+void CtrlSliderCursor::notifyLayout( int width, int height,
+                                     int xOffSet, int yOffSet )
+{
+    if( width > 0 && height > 0 )
+    {
+        CtrlGeneric::notifyLayout( width, height, xOffSet, yOffSet );
+    }
+    else
+    {
+        onPositionChange();
+        const Position *pPos = getPosition();
+        CtrlGeneric::notifyLayout( m_lastCursorRect.width,
+                                   m_lastCursorRect.height,
+                                   m_lastCursorRect.x - pPos->getLeft(),
+                                   m_lastCursorRect.y - pPos->getTop() );
+    }
+}
+
 void CtrlSliderCursor::onUpdate( Subject<VarPercent> &rVariable, void *arg  )
 {
     (void)rVariable; (void)arg;

modules/gui/skins2/controls/ctrl_slider.hpp

@@ -71,6 +71,10 @@ public:
     /// Method called when the control is resized
     virtual void onResize();
 
+    /// Method called to notify are to be updated
+    virtual void notifyLayout( int witdh = -1, int height = -1,
+                               int xOffSet = 0, int yOffSet = 0 );
+
     /// Get the text of the tooltip
     virtual UString getTooltipText() const { return m_tooltip; }