Don't shop-donate non-empty bags dropped in sellobj_state SELL_DONTSELL

Don't shop-donate non-empty bags dropped in sellobj_state SELL_DONTSELL

For a shop to NOT charge for an object, two conditions apply:

 1. The object's `no_charge` flag must be set.
 2. That `no_charge` flag must be set regardless of whether or not the
    shop typically sells the object in question.

There are two places in `sellobj()` which ignore the second condition,
thus transferring object ownership from the player to the shop without
the player's consent:

 1. A container is dropped in a shop that typically sells such
    containers and `sellobj_state` is `SELL_DONTSELL`.
 2. A zero-cost container holding nothing but gold is dropped in a shop
    that typically sells such containers.

Neither occurs currently in NetHack: the latter because NetHack has no
zero-cost containers, but the former is needed for an upcoming bug fix.

This may be related to SC343-21: "Accounting is incorrect for containers
dropped in a shop that does not sell them."

Based on DynaHack commit 4e79b6a (Don't shop-donate non-empty bags
dropped in sellobj_state SELL_DONTSELL) by me.