Entity: fixed not calculating surrounding blocks on entity creation

it's unclear if this was actually causing any bugs, but if it was it would likely manifest in the form of, for example, not burning in lava.

src/pocketmine/entity/Entity.php

@@ -461,7 +461,7 @@ abstract class Entity extends Location implements Metadatable, EntityIds{
 	protected $lastDamageCause = null;
 
 	/** @var Block[]|null */
-	protected $blocksAround = [];
+	protected $blocksAround = null;
 
 	/** @var float|null */
 	public $lastX = null;