Fixes a runtime in "reference decoder" circuit (#35754)

* Adds "safe" option to hextostr and hex2num

* Fixes a runtime in ICs

code/__HELPERS/type2type.dm

@@ -12,7 +12,8 @@
 //Returns an integer given a hex input, supports negative values "-ff"
 //skips preceding invalid characters
 //breaks when hittin invalid characters thereafter
-/proc/hex2num(hex)
+// If safe=TRUE, returns null on incorrect input strings instead of CRASHing
+/proc/hex2num(hex, safe=FALSE)
 	. = 0
 	var/place = 1
 	for(var/i in length(hex) to 1 step -1)
@@ -26,6 +27,9 @@
 				num -= 55	//A-F
 			if(45)
 				return . * -1 // -
+			else
+				if(safe)
+					return null
 				else
 					CRASH("Malformed hex number")
 
@@ -582,12 +586,16 @@
 		r+= num2hex(c)
 	return r
 
-/proc/hextostr(str)
+// Decodes hex to raw byte string.
+// If safe=TRUE, returns null on incorrect input strings instead of CRASHing
+/proc/hextostr(str, safe=FALSE)
 	if(!istext(str)||!str)
 		return
 	var/r
 	var/c
 	for(var/i = 1 to length(str)/2)
-		c= hex2num(copytext(str,i*2-1,i*2+1))
+		c = hex2num(copytext(str,i*2-1,i*2+1), safe)
+		if(isnull(c))
+			return null
 		r += ascii2text(c)
 	return r

code/modules/integrated_electronics/subtypes/converters.dm

@@ -97,7 +97,7 @@
 
 /obj/item/integrated_circuit/converter/refdecode/do_work()
 	pull_data()
-	dec=XorEncrypt(hextostr(get_pin_data(IC_INPUT, 1)),SScircuit.cipherkey)
+	dec = XorEncrypt(hextostr(get_pin_data(IC_INPUT, 1), TRUE), SScircuit.cipherkey)
 	set_pin_data(IC_OUTPUT, 1, WEAKREF(locate(dec)))
 	push_data()
 	activate_pin(2)