Less fat zombies
In the advanced inventory, recognize when the player is not grabbing anything.

This is particularly troublesome in the following scenario:
* grab something (a shopping cart)
* Enter AIM
* Assign a pane to be [D]
* Exit the AIM
* Release the cart
* Enter AIM
* You can't easily switch slot on the pane assigned to be the [D]
Merge Adv inventory pane management fix.
Merge reduction in spawn rate for fat zombies.