Small Changes to Air Tanks

Changes the sprite for "double_nitrogen" from double phoron (why did it share the sprite?) to it's own sprite.
Makes double tanks properly doubled by ensuring they're *double* extended tanks. (normal emergency tanks have 2, extended have 6, double had 10, now 12.

code/game/objects/items/weapons/tanks/tank_types_vr.dm

@@ -6,7 +6,7 @@
 	icon_state = "emergency_double_vox"
 	gauge_icon = "indicator_double"
 	gauge_cap = 3
-	volume = 10
+	volume = 12		// CHOMP EDIT double extended
 
 /obj/item/weapon/tank/emergency/phoron/double/New()
 	..()
@@ -72,12 +72,14 @@
 	icon = 'icons/obj/tank_vr.dmi'
 	icon_state = "emergency_nitrogen"
 	gauge_icon = "indicator_smalltank"
+	volume = 6			// CHOMP EDIT adds a custom volume to ensure things aren't buggy with changes
 	gauge_cap = 3
 
 /obj/item/weapon/tank/emergency/nitrogen/double
 	icon = 'icons/obj/tank_vr.dmi'
-	icon_state = "emergency_double_vox"
+	icon_state = "emergency_double_vox_old"		// CHOMP EDIT using the old red double sprite to indicate double nitrogen rather than sharing the phoron tank (cuz why share the phoron tank?)
 	gauge_icon = "indicator_double"
+	volume = 12		// CHOMP EDIT double extended
 	gauge_cap = 3
 
 /obj/item/weapon/tank/emergency/phoron