Save and restore GtkStyleContext in a few places that were not doing it

Does not fix any known problem, but seems prudent

src/gtk/control.cpp

@@ -250,12 +250,14 @@ wxControl::GetDefaultAttributesFromGTKWidget(GtkWidget* widget,
         stateFlag = GTK_STATE_FLAG_ACTIVE;
     }
     GtkStyleContext* sc = gtk_widget_get_style_context(widget);
+    gtk_style_context_save(sc);
     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);
+    gtk_style_context_restore(sc);
     attr.colFg = wxColour(*fc);
     attr.colBg = wxColour(*bc);
     attr.font = wxFont(info);