Describe the bug
If the Gristmill menu is opened by a player but the Gristmill is destroyed while they are still in the menu (e.g. via an explosion or another player breaking it), the menu will remain open.

Version Information
Minecraft Version - 1.21.1
Mod Version - 2.0.5

Additional context
The menu remains active and players are still able to take items out of it, even though those same items would have already been dropped in-world when the Gristmill was removed.