Re-fix AIM move-all

[Qrox]

Summary

SUMMARY: Bugfixes "Fix AIM move-all only moving items from one direction (again)"

Purpose of change

Fixes #33633. It was either a bad merge, or someone thought it was okay to merge the two if statements...

Describe the solution

Used a different logic @ZhilkinSerg suggested below, and added a couple notes to make it clear to further maintainers.

[ZhilkinSerg]

Maybe do something like this?

    if( g->u.activity.targets.empty() ) {
        g->u.cancel_activity();
    }
    // TODO: Move this to advanced inventory instead of hacking it in here
    if( !keep_going ) {
        g->u.cancel_activity();
        cancel_aim_processing();
    }

[Qrox]

Yes, that makes the logic clearer, thank. I also changed it a bit to avoid possible double-invocation of cancel_activity().