deref addr's in list of atom_codes (#484)

src/prolog/machine/system_calls.rs

@@ -960,6 +960,8 @@ impl MachineState {
                                 let mut chars = String::new();
 
                                 for addr in addrs {
+                                    let addr = self.store(self.deref(addr));
+
                                     match Number::try_from((addr, &self.heap)) {
                                         Ok(Number::Fixnum(n)) => {
                                             match u32::try_from(n) {