Band-aids three runtimes (#4591)

* Runtime in dna_modifier.dm,330: Cannot read null.occupant

* Runtime in Chemistry-Reagents.dm,47: Cannot execute null.remove reagent().

* Runtime in blood.dm,182: Division by zero

* Compiled with the right map this time

code/modules/organs/blood.dm

@@ -141,7 +141,7 @@ var/const/CE_STABLE_THRESHOLD = 0.5
 
 		//Bleeding out
 		var/blood_max = 0
-		var/blood_loss_divisor = 30	//lower factor = more blood loss
+		var/blood_loss_divisor = 30.01	//lower factor = more blood loss
 
 		// Some species bleed out differently
 		blood_loss_divisor /= species.bloodloss_rate

code/modules/reagents/Chemistry-Reagents.dm

@@ -44,7 +44,8 @@
 	var/list/glass_special = null // null equivalent to list()
 
 /datum/reagent/proc/remove_self(var/amount) // Shortcut
-	holder.remove_reagent(id, amount)
+	if(holder)
+		holder.remove_reagent(id, amount)
 
 // This doesn't apply to skin contact - this is for, e.g. extinguishers and sprays. The difference is that reagent is not directly on the mob's skin - it might just be on their clothing.
 /datum/reagent/proc/touch_mob(var/mob/M, var/amount)