Fix normal crafted medbots being invisible (#89427)

## About The Pull Request
the comment lies, the skin var is no longer null safe
medibots crafted with a non-special medkit would give it a null skin,
which is no longer supported after they were reskinned
## Why It's Good For The Game
👻 
## Changelog
🆑
fix: crafted medibots are more consistently corporeal
/🆑

code/game/objects/items/storage/medkit.dm

@@ -447,8 +447,7 @@
 
 /// Gets what skin (icon_state) this medkit uses for a medbot
 /obj/item/storage/medkit/proc/get_medbot_skin()
-	// The skin var is nullsafe so returning nothing is A-OK
-	return
+	return "generic"
 
 /*
  * Pill Bottles