Don't choke on NULL pointer passed into wxSlider::GetSize.

Take the inverted coordinate system into account when computing size.


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_4_BRANCH@27066 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/os2/slider.cpp

@@ -863,8 +863,10 @@ void wxSlider::GetSize(
         wxFindMaxSize( m_hStaticValue
                       ,&vRect
                      );
-    *pnWidth  = vRect.xRight - vRect.xLeft;
-    *pnHeight = vRect.yBottom - vRect.yTop;
+    if (pnWidth)
+        *pnWidth  = vRect.xRight - vRect.xLeft;
+    if (pnHeight)
+        *pnHeight = vRect.yTop - vRect.yBottom;
 } // end of wxSlider::GetSize
 
 int wxSlider::GetThumbLength() const