Fixed gun executions (#3253)

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## About The Pull Request

Fixes executions. Also fired off a few other rounds to make sure nothing
else was wonky.

No Kepori were actually harmed in the making of this film. 

![dreamseeker_W5IavcWlZT](https://github.com/user-attachments/assets/81aa66eb-41d1-46ba-8633-d9d822d111fb)

There was a circular logic issue that arose with the gun.dm refactor
from a couple months ago and that's what was causing the issue.

Fixes #3252

## Why It's Good For The Game

Intended feature is working again

## Changelog

:cl:
fix: Executing someone with a gun is back, you psychos. Paint the floor
red!
/:cl:

code/modules/projectiles/gun.dm

@@ -773,7 +773,7 @@
 	if(chambered && chambered.BB && can_trigger_gun(user))
 		chambered.BB.damage *= 3
 		//Check is here for safeties and such, brain will be removed after
-		if(!pre_fire(target, user, TRUE, params, BODY_ZONE_HEAD))
+		if(!pre_fire(target, user, TRUE, FALSE, params, BODY_ZONE_HEAD)) // We're already in handle_suicide, hence the 4th parameter needs to be FALSE to avoid circular logic. Also, BODY_ZONE_HEAD because we want to damage the head as a whole.
 			return
 
 		var/obj/item/organ/brain/brain_to_blast = target.getorganslot(ORGAN_SLOT_BRAIN)