Fix #82, empty object breaks GetPlayerSummaries

Author: nicekiwi

src/Syntax/SteamApi/Steam/User.php

@@ -162,7 +162,9 @@ protected function convertToObjects($players)
         $cleanedPlayers = [];
 
         foreach ($players as $player) {
-            $cleanedPlayers[] = new PlayerContainer($player);
+            if(property_exists($player, 'steamid')) {
+                $cleanedPlayers[] = new PlayerContainer($player);
+            }
         }
 
         return $cleanedPlayers;