added wxDialog::GetParentForModalDialog() and use it to try to always create modal dialogs with a parent (slightly modified patch 1702962)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@45588 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/msgdlg.cpp

@@ -38,7 +38,8 @@ wxMessageDialog::wxMessageDialog(wxWindow *parent,
     m_caption = caption;
     m_message = message;
     SetMessageDialogStyle(style);
-    m_parent = wxGetTopLevelParent(parent);
+
+    m_parent = GetParentForModalDialog(parent);
 
     GtkMessageType type = GTK_MESSAGE_ERROR;
     GtkButtonsType buttons = GTK_BUTTONS_OK;