[MIRROR] Refactors roundstart centcom threat report. (#2739)

* Refactors roundstart centcom threat report.

* Update blob.dm

* Update changeling.dm

* Update traitor_chan.dm

* Update sandbox.dm

* Update traitor.dm

code/__HELPERS/_lists.dm

@@ -205,6 +205,22 @@
 
 	return null
 
+/proc/pickweightAllowZero(list/L) //The original pickweight proc will sometimes pick entries with zero weight.  I'm not sure if changing the original will break anything, so I left it be.
+	var/total = 0
+	var/item
+	for (item in L)
+		if (!L[item])
+			L[item] = 0
+		total += L[item]
+
+	total = rand(0, total)
+	for (item in L)
+		total -=L [item]
+		if (total <= 0 && L[item])
+			return item
+
+	return null
+
 //Pick a random element from the list and remove it from the list.
 /proc/pick_n_take(list/L)
 	if(L.len)