Exit the adv. inv. after starting an activity

In response to #6988:

Reloading is an activity. One has to leave the adv. inventory after starting to reload. Same applies to other activities like fishing / disassembling / ...

This PR leaves the adv. inv. automatically if the player has started an activity. This is also important as many activities use items in the inventory and store their position index. Further adv. inv. handling could change them.