Avoid "Gtk-WARNING **: State doesn't match"

See https://github.com/wxWidgets/wxWidgets/pull/232

src/gtk/control.cpp

@@ -252,6 +252,7 @@ wxControl::GetDefaultAttributesFromGTKWidget(GtkWidget* widget,
     GtkStyleContext* sc = gtk_widget_get_style_context(widget);
     GdkRGBA *fc, *bc;
     wxNativeFontInfo info;
+    gtk_style_context_set_state(sc, stateFlag);
     gtk_style_context_get(sc, stateFlag,
         "color", &fc, "background-color", &bc,
         GTK_STYLE_PROPERTY_FONT, &info.description, NULL);