refactor: add TileLayer.initLoader()

- need to initialize worker thread after (super) class is constructed

vtm/src/org/oscim/layers/tile/TileLayer.java

@@ -53,15 +53,18 @@ public abstract class TileLayer<T extends TileLoader> extends Layer implements M
 
 		// Instantiate TileLoader threads
 		mTileLoader = new ArrayList<T>();
+
+		// RenderLayer is working in GL Thread and actually
+		// drawing loaded tiles to screen.
+		mRenderer = mRenderLayer = new TileRenderer(mTileManager);
+	}
+
+	protected void initLoader() {
 		for (int i = 0; i < mNumTileLoader; i++) {
 			T tileGenerator = createLoader(mTileManager);
 			mTileLoader.add(tileGenerator);
 			tileGenerator.start();
 		}
-
-		// RenderLayer is working in GL Thread and actually
-		// drawing loaded tiles to screen.
-		mRenderer = mRenderLayer = new TileRenderer(mTileManager);
 	}
 
 	abstract protected T createLoader(TileManager tm);

vtm/src/org/oscim/layers/tile/bitmap/BitmapTileLayer.java

@@ -58,6 +58,7 @@ public class BitmapTileLayer extends TileLayer<TileLoader> {
 		super(map, tileSource.getZoomLevelMin(), tileSource.getZoomLevelMax(), cacheLimit);
 		mTileSource = tileSource;
 		mFade = mTileSource.getFadeSteps();
+		initLoader();
 	}
 
 	@Override

vtm/src/org/oscim/layers/tile/vector/VectorTileLayer.java

@@ -39,10 +39,12 @@ public class VectorTileLayer extends TileLayer<VectorTileLoader> {
 
 	public VectorTileLayer(Map map) {
 		super(map);
+		initLoader();
 	}
 
 	public VectorTileLayer(Map map, int minZoom, int maxZoom, int cacheLimit) {
 		super(map, minZoom, maxZoom, cacheLimit);
+		initLoader();
 	}
 
 	@Override