Fixed IsShownOnScreen() for Mac

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@51996 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/mac/carbon/window.cpp

@@ -3219,3 +3219,8 @@ wxByte wxWindowMac::GetTransparent() const
 {
     return m_macAlpha ;
 }
+
+bool wxWindowMac::IsShownOnScreen() const
+{
+    return ((wxWindowMac*)this)->MacIsReallyShown();
+}