Avoid GTK+ errors when using AUI wxPseudoTransparentFrame hack.

Avoid GTK+ errors when using AUI wxPseudoTransparentFrame hack.

wxPseudoTransparentFrame is not a top level window at all and the code in
wxGTK wxTopLevelWindow::DoSetSizeHints() fails for it when it is called from
wxWindowBase::CreateBase() because of it and spits GTK+ errors as it calls
gtk_window_set_geometry_hints() with NULL widget.

Fix this by simply skipping wxTopLevelWindow implementation of this method in
wxPseudoTransparentFrame. A better fix would be to get rid of this hack
completely, of course.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62896 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775