fix #200. Track palace building id on update

Author: dalerank

src/building/building_palace.cpp

@@ -53,6 +53,10 @@ void building_palace::on_destroy() {
     g_city.buildings.remove_palace(base);
 }
 
+void building_palace::update_count() const {
+    g_city.buildings.track_building(base, true);
+}
+
 bool building_palace::can_play_animation() const {
     return worker_percentage() > 50;
 }

src/building/building_palace.h

@@ -10,6 +10,7 @@ class building_palace : public building_impl {
     virtual void on_create(int orientation) override;
     virtual void on_post_load() override;
     virtual void on_destroy() override;
+    virtual void update_count() const override;
     virtual bool can_play_animation() const override;
     virtual void update_graphic() override;
     virtual void draw_tooltip(tooltip_context *c) override;