Fix error if Steam returns empty response

Querying the API for a Steam user who hastheir gameplay history private returns:
`"response": {}`
which results in the error:
`Undefined property: stdClass::$total_count in Player.php on line 120`

src/Syntax/SteamApi/Steam/Player.php

@@ -111,7 +111,7 @@ public function GetRecentlyPlayedGames($count = null)
         // Get the client
         $client = $this->getServiceResponse($arguments);
 
-        if ($client->total_count > 0) {
+        if (isset($client->total_count) && $client->total_count > 0) {
             // Clean up the games
             $games = $this->convertToObjects($client->games);