Items saved in player inventory on server crash.

[NicoNekoDev]

If a server crashes while a player have a split window open, the items remains in their inventory.

Steps to reproduce:

1. create a split window, fill the bottom with items, and open it
2. go to console and do a /save-all (keep the gui open!)
3. crash the server (keep the gui open!) - one way is killing the java process manually

What is observed is that after the restart, the player has the gui items in their inventory and they can play with them. Also, their previous inventory is not restored, so RIP items if the player has any.