Fixes 0 value not being saved in constant memory circuits (#36867)

* Fixes 0 value not being saved in constant memory circuits

* Fixes 0 value not being loaded in constant memory circuits

* Switched to isnull proc for null checks

code/modules/integrated_electronics/core/saved_circuits.dm

@@ -40,7 +40,7 @@
 			component_params["inputs"] = saved_inputs
 
 	var/special = save_special()
-	if(special)
+	if(!isnull(special))
 		component_params["special"] = special
 
 	return component_params
@@ -107,7 +107,7 @@
 			pin.write_data_to_pin(input_value)
 			// TODO: support for special input types, such as internal refs and maybe typepaths
 
-	if(component_params["special"])
+	if(!isnull(component_params["special"]))
 		load_special(component_params["special"])
 
 /obj/item/integrated_circuit/proc/load_special(special_data)