InventoryDoubleUpdateFix

There is an exception going around in our server that crashes the game for almost all players when it happens

It reads something like this:

System.NullReferenceException: Object reference not set to an instance of an object. at Vintagestory.Common.InventoryNetworkUtil.UpdateSlotStack(ItemSlot slot, ItemStack newStack) in VintagestoryLib\Common\GameContent\Inventory\InventoryNetworkUtil.cs:line 493 at Vintagestory.Client.NoObf.GeneralPacketHandler.HandleInventoryDoubleUpdate(Packet_Server packet) in VintagestoryLib\Client\Systems\GeneralPacketHandler.cs:line 385 at Vintagestory.Client.NoObf.ClientMain.ExecuteMainThreadTasks(Single deltaTime) in VintagestoryLib\Client\ClientMain.cs:line 786 at Vintagestory.Client.GuiScreenRunningGame.RenderToPrimary(Single dt) in VintagestoryLib\Client\MainMenu\Screens\GuiScreenRunningGame.cs:line 161 at Vintagestory.Client.ScreenManager.Render(Single dt) in VintagestoryLib\Client\ScreenManager.cs:line 695 at Vintagestory.Client.ScreenManager.OnNewFrame(Single dt) in VintagestoryLib\Client\ScreenManager.cs:line 670 at Vintagestory.Client.NoObf.ClientPlatformWindows.window_RenderFrame(FrameEventArgs e) in VintagestoryLib\Client\ClientPlatform\GameWindow.cs:line 88 at OpenTK.Windowing.Desktop.GameWindow.Run()

It has something to do with swapping items in your inventory (I suspect it might be Art of Growing that causes this), but I am unable to pinpoint the exact issue. So I have decided to create a small patch that consumes the exception and logs info about the error into the client logs. 

Is swallowing exceptions a good idea? Not at all. But it is a lot better than half the server crashing a few times every day.