Fix terrain

h3d/scene/pbr/terrain/Terrain.hx

@@ -120,6 +120,7 @@ class Terrain extends Object {
 		var tile = getTile(x,y);
 		if(tile == null){
 			tile = new Tile(x, y, this);
+			tile.refreshMesh();
 			tile.refresh();
 			tiles.push(tile);
 		}

h3d/scene/pbr/terrain/Tile.hx

@@ -539,6 +539,8 @@ class Tile extends h3d.scene.Mesh {
 	}
 
 	function isReady(){
+		if(primitive == null)
+			return false;
 		if( getTerrain().surfaceArray == null || getTerrain().surfaces.length == 0 || surfaceWeights.length != getTerrain().surfaces.length)
 			return false;
 		if( heightMap == null )