Fixed crashes and errors when loading into world.

Source/Game/Entities/Object/Update/UpdateField.cs

@@ -382,7 +382,7 @@ namespace Game.Entities
 
         public void ClearChangesMask<U>(OptionalUpdateField<U> updateField) where U : new()
         {
-            if (typeof(IHasChangesMask).IsAssignableFrom(typeof(U)))
+            if (typeof(IHasChangesMask).IsAssignableFrom(typeof(U)) && updateField.HasValue())
                 ((IHasChangesMask)updateField._value).ClearChangesMask();
         }
 

Source/Game/Entities/Object/WorldObject.cs

@@ -2981,9 +2981,9 @@ namespace Game.Entities
         public bool IsPermanentWorldObject() { return m_isWorldObject; }
 
         public ITransport GetTransport() { return m_transport; }
-        public T GetTransport<T>() where T : ITransport
+        public T GetTransport<T>() where T : class, ITransport
         {
-            return (T)m_transport;
+            return m_transport as T;
         }
         public float GetTransOffsetX() { return m_movementInfo.transport.pos.GetPositionX(); }
         public float GetTransOffsetY() { return m_movementInfo.transport.pos.GetPositionY(); }