Accept null for targets in Human->sendSkin()

For humans, it'll send to all viewers. For players, it'll send to all viewers, and the player itself.

src/pocketmine/Player.php

@@ -762,6 +762,20 @@ class Player extends Human implements CommandSender, ChunkLoader, IPlayer{
 		return true;
 	}
 
+	/**
+	 * {@inheritdoc}
+	 *
+	 * If null is given, will additionally send the skin to the player itself as well as its viewers.
+	 */
+	public function sendSkin(array $targets = null) : void{
+		if($targets === null){
+			$targets = $this->hasSpawned;
+			$targets[] = $this;
+		}
+
+		parent::sendSkin($targets);
+	}
+
 	/**
 	 * Gets the player IP address
 	 *