make sure we retain shared state when destructing the map object

refs #261

src/map/tile_data.cpp

@@ -56,12 +56,23 @@ void TileData::cancel() {
     }
 }
 
+void TileData::beforeParse() {}
+
 void TileData::reparse() {
+    beforeParse();
+
     // We're creating a new work request. The work request deletes itself after it executed
     // the after work handler
     new uv::work<std::shared_ptr<TileData>>(
         map.getLoop(),
-        [](std::shared_ptr<TileData> &tile) { tile->parse(); },
-        [](std::shared_ptr<TileData> &tile) { tile->map.update(); },
+        [](std::shared_ptr<TileData> &tile) {
+            tile->parse();
+        },
+        [](std::shared_ptr<TileData> &tile) {
+            tile->afterParse();
+            tile->map.update();
+        },
         shared_from_this());
 }
+
+void TileData::afterParse() {}