SKM-24u LMG Modification on the Black Market (shiptest-ss13#3871)

## About The Pull Request

Adds the SKM-24u LMG Modification to the black market, for on average
about 1000 above standard SKM sale price. Given the statistical
similarities to the regular SKM minus it's having of a bipod and the
non-guarantee of drum magazines, this felt right.

Also fixes bipods to actually work at all after the code for them was
just outright removed in a PR I can't care to find.

## Why It's Good For The Game

New rare weapons variety to the black market, and a defensive option in
the form of a bipod-attached LMG should make for some interesting
situations.

## Changelog

:cl:
add: An intercepted shipment of CM-40 barrels has led to an influx of
SKM-24u LMGs to the black market. Report sightings to your nearest CLIP
representative.
fix: Bipods actually work now.
/:cl:

---------

Signed-off-by: firebudgy <[email protected]>

code/modules/cargo/blackmarket/blackmarket_items/weapons.dm

@@ -425,3 +425,14 @@
 	stock_min = 1
 	stock_max = 5
 	availability_prob = 10
+
+/datum/blackmarket_item/weapon/skm_lmg
+	name = "SKM-24u Light Machinegun"
+	desc = "Your regular rifles not have enough oomph for you? This SKM-24 was converted with help from a 'liberated' CM-40 parts shipment into a light machinegun, ready to blow away whatever you point it at. Increased firerate makes it buck like a mule, so keep that bipod on the ground. Drums sold separately!"
+	item = /obj/item/gun/ballistic/automatic/hmg/skm_lmg
+
+	price_min = 5000
+	price_max = 7000
+	stock_max = 2
+	availability_prob = 15
+	spawn_weighting = FALSE

code/modules/projectiles/guns/ballistic/hmg.dm

@@ -65,6 +65,22 @@
 	else
 		retract_bipod(user=user)
 
+/obj/item/gun/ballistic/automatic/hmg/calculate_recoil(mob/user, recoil_bonus = 0)
+	var/total_recoil = recoil_bonus
+
+	if(bipod_deployed)
+		total_recoil += deploy_recoil_bonus
+
+	return ..(user, total_recoil)
+
+/obj/item/gun/ballistic/automatic/hmg/calculate_spread(mob/user, bonus_spread)
+	var/total_spread = bonus_spread
+
+	if(bipod_deployed)
+		total_spread += deploy_spread_bonus
+
+	return ..(user, total_spread)
+
 /obj/item/gun/ballistic/automatic/hmg/proc/deploy_bipod(mob/user)
 	//we check if we can actually deploy the thing
 	var/can_deploy = TRUE