Changed way CPR lock works, no dependancy on world time.stored time now.

When someone starts doing CPR, it locks. After 3 ticks after CPR is done it unlocks. No other mobs can do CPR on same mob while it is locked.
((also it's one of places that can make CPR not start so I wanted ot replace timer with more simple semaphore))

code/modules/mob/living/carbon/human/inventory.dm

@@ -433,8 +433,9 @@
 						return
 				message = "\red <B>[source] is trying to empty [target]'s pockets.</B>"
 			if("CPR")
-				if (target.cpr_time >= world.time + 3)
+				if (!target.cpr_time)
 					del(src)
+				target.cpr_time = 0
 				message = "\red <B>[source] is trying perform CPR on [target]!</B>"
 			if("id")
 				message = "\red <B>[source] is trying to take off [target.wear_id] from [target]'s uniform!</B>"
@@ -540,10 +541,7 @@ It can still be worn/put on as normal.
 			if (target.legcuffed)
 				strip_item = target.legcuffed
 		if("CPR")
-			if (target.cpr_time >= world.time + 30)
-				del(src)
 			if ((target.health >= -99.0 && target.health <= 0))
-				target.cpr_time = world.time
 				var/suff = min(target.getOxyLoss(), 7)
 				target.adjustOxyLoss(-suff)
 				target.updatehealth()
@@ -551,6 +549,8 @@ It can still be worn/put on as normal.
 					O.show_message("\red [source] performs CPR on [target]!", 1)
 				target << "\blue <b>You feel a breath of fresh air enter your lungs. It feels good.</b>"
 				source << "\red Repeat at least every 7 seconds."
+				spawn(3)
+					target.cpr_time = 1
 		if("dnainjector")
 			var/obj/item/weapon/dnainjector/S = item
 			if(S)