fix(virology): machinery fixes

PR #11112

code/modules/virus2/centrifuge.dm

@@ -106,13 +106,15 @@
 	..()
 	if (stat & (NOPOWER|BROKEN)) return
 
-	if (curing)
+	if(curing)
 		curing -= speed
-		if (curing <= 0)
+		curing = max(curing, 0)
+		if(curing <= 0)
 			cure()
 
-	if (isolating)
+	if(isolating)
 		isolating -= speed
+		isolating = max(isolating, 0)
 		if(isolating <= 0)
 			isolate()
 
@@ -136,6 +138,9 @@
 		if (B)
 			var/datum/disease2/disease/virus = locate(href_list["isolate"])
 			virus2 = virus.getcopy()
+			if(!virus2)
+				return TOPIC_HANDLED
+
 			isolating = 40
 			update_icon()
 		return TOPIC_REFRESH
@@ -169,12 +174,15 @@
 			return TOPIC_REFRESH
 
 /obj/machinery/computer/centrifuge/proc/cure()
-	if (!sample) return
+	if(!sample)
+		return
+
 	var/datum/reagent/blood/B = locate(/datum/reagent/blood) in sample.reagents.reagent_list
-	if (!B) return
+	if(!B)
+		return
 
 	var/list/data = list("antibodies" = B.data["antibodies"])
-	var/amt= sample.reagents.get_reagent_amount(/datum/reagent/blood)
+	var/amt = sample.reagents.get_reagent_amount(/datum/reagent/blood)
 	sample.reagents.remove_reagent(/datum/reagent/blood, amt)
 	sample.reagents.add_reagent(/datum/reagent/antibodies, amt, data)
 
@@ -183,11 +191,13 @@
 	ping("\The [src] pings, \"Antibody isolated.\"")
 
 /obj/machinery/computer/centrifuge/proc/isolate()
-	if (!sample) return
+	if(!sample || !virus2)
+		return
+
 	var/obj/item/virusdish/dish = new /obj/item/virusdish(loc)
 	dish.virus2 = virus2
 	dish.virus2.infected = null
-	virus2 = null
+	QDEL_NULL(virus2)
 
 	SSnano.update_uis(src)
 	update_icon()

code/modules/virus2/diseasesplicer.dm

@@ -113,19 +113,22 @@
 		return
 
 	if(scanning)
-		scanning -= 1*speed
+		scanning -= 1 * speed
+		scanning = max(scanning, 0)
 		if(scanning <= 0)
 			ping("\The [src] pings, \"Analysis complete.\"")
 			SSnano.update_uis(src)
 
 	if(splicing)
-		splicing -= 1*speed
+		splicing -= 1 * speed
+		splicing = max(splicing, 0)
 		if(splicing <= 0)
 			ping("\The [src] pings, \"Splicing operation complete.\"")
 			SSnano.update_uis(src)
 
 	if(burning)
-		burning -= 1*speed
+		burning -= 1 * speed
+		burning = max(burning, 0)
 		if(burning <= 0)
 			var/obj/item/diseasedisk/d = new /obj/item/diseasedisk(src.loc)
 			d.analysed = analysed

code/modules/virus2/items_devices.dm

@@ -62,7 +62,7 @@
 	..()
 	if(prob(50))
 		to_chat(user, "<span class='danger'>\The [src] shatters!</span>")
-		if(virus2.infectionchance > 0)
+		if(virus2?.infectionchance > 0)
 			for(var/mob/living/carbon/target in view(1, get_turf(src)))
 				if(airborne_can_reach(get_turf(src), get_turf(target)))
 					infect_virus2(target, src.virus2)