Fixed IsShownOnScreen() for Mac

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@51995 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/wincmn.cpp

@@ -891,8 +891,12 @@ bool wxWindowBase::Enable(bool enable)
 
 bool wxWindowBase::IsShownOnScreen() const
 {
+#ifdef __WXMAC__
+    return ((wxWindowMac*)this)->MacIsReallyShown();
+#else
     return IsShown() &&
            (GetParent() == NULL || GetParent()->IsShownOnScreen());
+#endif
 }
 
 // ----------------------------------------------------------------------------