return true from IsShownOnScreen() for TLWs even if their parent is hidden [backport of r50876 from trunk]

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@52095 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/wincmn.cpp

@@ -891,12 +891,11 @@ bool wxWindowBase::Enable(bool enable)
 
 bool wxWindowBase::IsShownOnScreen() const
 {
-#ifdef __WXMAC__
-    return ((wxWindowMac*)this)->MacIsReallyShown();
-#else
+    // A window is shown on screen if it itself is shown and so are all its
+    // parents. But if a window is toplevel one, then its always visible on
+    // screen if IsShown() returns true, even if it has a hidden parent.
     return IsShown() &&
-           (GetParent() == NULL || GetParent()->IsShownOnScreen());
-#endif
+           (IsTopLevel() || !GetParent() || GetParent()->IsShownOnScreen());
 }
 
 // ----------------------------------------------------------------------------