Equipping 2 UPS on different legs causes UPS welder to fail when crafting with it

# Describe the bug

Putting 2 UPS on the same leg, then switching one to the other leg results in crafting with a modded arc welder (UPS mod) saying `You no longer have a none and can't continue crafting` until you remove one of the UPS and reload your game

# Steps To Reproduce

1. Wear 2 crafted UPS on same leg (left)
2. Mod makeshift electric welder with UPS conversion mod
3. After starting a craft requiring the welder (which shows green in required tools) notice the error message, `You no longer have a none and can't continue crafting`
4. Try moving around UPS to no avail
5. remove 1 equipped UPS and restart game
6. crafting now works.

# Expected behavior

Equipping multiple UPS on different legs should function the same as equipping them on the same leg.

# Versions and configuration

- OS: Ubuntu 18.04.4 LTS
- Game Version: 0.E-2 [64-bit]
- Graphics version: Tiles
- Ingame language: English
- Mods loaded: dda, no_npc_food, sees_player_retro, aftershock, crt_expansion, magiclysm

# Additional context