Fix third-party not premium player detection

bukkit/src/main/java/com/github/games647/fastlogin/bukkit/MojangApiBukkit.java

@@ -80,6 +80,10 @@ public class MojangApiBukkit extends MojangApiConnector {
         }
 
         String uuid = (String) mojangPlayer.get("id");
+        if (uuid == null || uuid.equals("null")) {
+            return null;
+        }
+        
         return FastLoginCore.parseId(uuid);
     }
 }

bungee/src/main/java/com/github/games647/fastlogin/bungee/MojangApiBungee.java

@@ -28,6 +28,10 @@ public class MojangApiBungee extends MojangApiConnector {
             mojangPlayer = BungeeCord.getInstance().gson.fromJson(json, MojangPlayer.class);
         }
 
+        if (mojangPlayer.getId() == null || mojangPlayer.getId().equals("null")) {
+            return null;
+        }
+        
         return FastLoginCore.parseId(mojangPlayer.getId());
     }