Nested inventory + trading with NPC = counting items twice

[big-smitty]

Description

When trading with an NPC, you can sell a container and it's contents, then sell its contents, doubling the expected gain.

Steps To Reproduce

1. Trade with an NPC
2. Sell a container:
   
3. Sell the contents of the container, note the difference in credit, and the expected price of selling:
   

Expected behavior

Selling the container implies selling the contents, so you shouldn't be able to select the subcontents of a container if you are selling the container.
eg.
Selling a bottle of water -> you shouldn't be able to sell the water as well.
so the water would auto-select on selecting the bottle.

Versions and configuration

• OS: Win 10
• Version: experimental 38074ba, released 05/25/21@1559
• Graphics: Tiles
• Language: en-us
• Mods: Aftershock, stats through kills, Magiclysm

[natsirt721]

This works the other way around too - you can dupe items by buying the item and the container that it is in. See #48922

[RoyBerube]

PR #48580 addressed this kind of problem by disallowing a duplicate selection when in a container. The same approach should work here.