Fixed async light population producing garbage when generator isn't registered, closes #2488

src/pocketmine/block/BlockFactory.php

@@ -330,6 +330,10 @@ class BlockFactory{
 		}
 	}
 
+	public static function isInit() : bool{
+		return self::$fullList !== null;
+	}
+
 	/**
 	 * Registers a block type into the index. Plugins may use this method to register new block types or override
 	 * existing ones.