`professional_zombie_gear` item group can cause errors on monster death

[mqrause]

Describe the bug

It is possible a monster death can create an error message leading to CI test fails. https://github.com/CleverRaven/Cataclysm-DDA/runs/7653184359?check_suite_focus=true#step:16:430

Steps to reproduce

I have not been able to reproduce the issue with the seed from the failed test and in another 60 random test runs locally.

However digging into the test code I can fairly safely conclude the cause is the chance for professional_zombie_gear in the default_zombie_death_drops item group. professional_zombie_gear contains the group hardware_plumbing, which in turn contains plumbing_clothing which has the explicit comment "//2": "Not intended to be a set of clothing for NPCs or monsters", most likely because it does not guarantee in any way that proper container items are spawned for any additional loot to be put in, since it seems to only spawn one item from the list and not a set of gear the zombie would be wearing.

Expected behavior

Items spawn without issues. However in this case it might be unlikely enough to not be a problem.

Screenshots

No response

Versions and configuration

bc8d87c8203708c2580c89370a253e190f1ef7e4

Additional context

No response

[Stadler76]

I assume, that this one is related: https://github.com/CleverRaven/Cataclysm-DDA/runs/7708088941?check_suite_focus=true#step:16:259

[mqrause]

Presumably another case: https://github.com/CleverRaven/Cataclysm-DDA/runs/7868235039?check_suite_focus=true#step:16:568