Update railgun.dm (#4756)

Fixes a small bug where the blitzshell shotguns slug-shot has null charge cost and thus can't fire

code/modules/projectiles/guns/energy/projectile/railgun.dm

@@ -120,7 +120,7 @@
 	init_firemodes = list(
 		list(mode_name="Buckshot", mode_desc="Fires a buckshot synth-shell", projectile_type=/obj/item/projectile/bullet/pellet/shotgun, charge_cost=100, icon="kill"),
 		list(mode_name="Beanbag", mode_desc="Fires a beanbag synth-shell", projectile_type=/obj/item/projectile/bullet/shotgun/beanbag, charge_cost=25, icon="stun"),
-		list(mode_name="Blast", mode_desc="Fires a slug synth-shell", projectile_type=/obj/item/projectile/bullet/shotgun, charge_cost=null, icon="destroy"),
+		list(mode_name="Blast", mode_desc="Fires a slug synth-shell", projectile_type=/obj/item/projectile/bullet/shotgun, charge_cost=50, icon="destroy"),
 	)
 	serial_type = "GP"
 	gun_tags = list(GUN_PROJECTILE, GUN_LASER, GUN_ENERGY, GUN_SCOPE)