fix belts were not drawn

src/lib/sim/BuildingSystem.cpp

@@ -656,6 +656,21 @@ std::vector<ConstructionSite> BuildingSystem::allSites() const
                                          m_constructionQueue.end());
 }
 
+std::vector<BuildingSystem::BeltTileInfo> BuildingSystem::allBeltTiles() const
+{
+    std::vector<BeltTileInfo> result;
+    result.reserve(m_beltEntities.size());
+    for (const std::map<EntityId, BeltEntry>::value_type& kv : m_beltEntities)
+    {
+        BeltTileInfo info;
+        info.id   = kv.first;
+        info.tile = kv.second.tile;
+        info.type = kv.second.type;
+        result.push_back(info);
+    }
+    return result;
+}
+
 bool BuildingSystem::isTileOccupied(QPoint tile) const
 {
     return m_tileOccupancy.count({tile.x(), tile.y()}) > 0;