restored manual calls to gtk_glwindow_realized/map_callback() and added comment explaining why they're (sometimes) needed

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@32459 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/glcanvas.cpp

@@ -355,6 +355,15 @@ bool wxGLCanvas::Create( wxWindow *parent,
     gtk_widget_pop_visual();
     gtk_widget_pop_colormap();
 
+    // if our parent window is already visible, we had been realized before we
+    // connected to the "realize" signal and hence our m_glContext hasn't been
+    // initialized yet and we have to do it now
+    if (GTK_WIDGET_REALIZED(m_wxwindow))
+        gtk_glwindow_realized_callback( m_wxwindow, this );
+
+    if (GTK_WIDGET_MAPPED(m_wxwindow))
+        gtk_glwindow_map_callback( m_wxwindow, this );
+
     return TRUE;
 }