Fix crash when opening action menu with guns in inventory

[Qrox]

Summary

SUMMARY: Bugfixes "Fix crash when opening action menu with guns in inventory"

Purpose of change

Fixes #39403. item::get_use calls visit_items, which ignores the item content if it is a gun or magazine, whereas item::get_usable_item calls contents.visit_contents, which iterates over the item content regardless of the item type. So when initializing the action menu, item::get_usable_item returns the item content if it has the wanted use action, but item::get_use returns null if the item is a gun. Dereferencing the return value causes the game to crash.

Describe the solution

Use visit_items in item::get_usable_item so content of guns and magazines are ignored.

Testing

Loaded the attached save from #39403, opened item action menu, and the crash no longer happened.