Makes interacting with an assembly bomb interact with the assembly instead of opening the tank UI (#84075)

## About The Pull Request
Changes it so that interacting in hand with an assembly bomb will
interact with the assemble instead of opening the tank UI.
## Why It's Good For The Game
Currently when you interact with an assembly bomb in hand it opens the
tank UI instead of interacting with the assembly, which makes them
awkward to use as you have to configure the assembly before attaching it
to the tank and welding the tank.

Fixes #84073 
## Changelog
🆑
fix: Interacting with an assembly bomb in hand will now allow you to
interact with the attached assembly instead of opening the gas tank UI.
Right-clicking will display the gas tank UI instead.
/🆑

code/modules/assembly/mousetrap.dm

@@ -153,7 +153,7 @@
  * * user: The mob handling the trap
  */
 /obj/item/assembly/mousetrap/proc/clumsy_check(mob/living/carbon/human/user)
-	if(!armed)
+	if(!armed || !user)
 		return FALSE
 	if((HAS_TRAIT(user, TRAIT_DUMB) || HAS_TRAIT(user, TRAIT_CLUMSY)) && prob(50))
 		var/which_hand = BODY_ZONE_PRECISE_L_HAND