allow wxDialog::ShowModal() after Show() (see #1416, #4658, #4664)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@54328 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/dialog.cpp

@@ -99,7 +99,6 @@ void wxDialog::SetModal( bool WXUNUSED(flag) )
 int wxDialog::ShowModal()
 {
     wxASSERT_MSG( !IsModal(), "ShowModal() can't be called twice" );
-    wxASSERT_MSG( !IsShown(), "ShowModal() can't be called after Show()" );
 
     // release the mouse if it's currently captured as the window having it
     // will be disabled when this dialog is shown -- but will still keep the