Don't replace existing nodes in singlenode mapgen

src/mapgen_singlenode.cpp

@@ -72,13 +72,18 @@ void MapgenSinglenode::makeChunk(BlockMakeData *data) {
 	v3s16 node_max = (blockpos_max+v3s16(1,1,1))*MAP_BLOCKSIZE-v3s16(1,1,1);
 
 	content_t c_node = ndef->getId("mapgen_singlenode");
-	if(c_node == CONTENT_IGNORE)
+	if (c_node == CONTENT_IGNORE)
 		c_node = CONTENT_AIR;
-	for(s16 z=node_min.Z; z<=node_max.Z; z++)
-	for(s16 y=node_min.Y; y<=node_max.Y; y++)
-	for(s16 x=node_min.X; x<=node_max.X; x++)
-	{
-		data->vmanip->setNode(v3s16(x,y,z), MapNode(c_node));
+	
+	MapNode n_node(c_node);
+	int i = 0;
+	
+	for (s16 z=node_min.Z; z<=node_max.Z; z++)
+	for (s16 y=node_min.Y; y<=node_max.Y; y++)
+	for (s16 x=node_min.X; x<=node_max.X; x++) {
+		if (vm->m_data[i].getContent() == CONTENT_IGNORE)
+			vm->m_data[i] = n_node;
+		i++;
 	}
 
 	// Add top and bottom side of water to transforming_liquid queue