Extract expressions in construct_ntor_key_map()

No behavioral change here: this is just refactoring.

src/feature/relay/router.c

@@ -278,19 +278,16 @@ construct_ntor_key_map(void)
 {
   di_digest256_map_t *m = NULL;
 
-  if (!tor_mem_is_zero((const char*)
-                       curve25519_onion_key.pubkey.public_key,
-                       CURVE25519_PUBKEY_LEN)) {
-    dimap_add_entry(&m,
-                    curve25519_onion_key.pubkey.public_key,
+  const uint8_t *cur_pk = curve25519_onion_key.pubkey.public_key;
+  const uint8_t *last_pk = last_curve25519_onion_key.pubkey.public_key;
+
+  if (!tor_mem_is_zero((const char *)cur_pk, CURVE25519_PUBKEY_LEN)) {
+    dimap_add_entry(&m, cur_pk,
                     tor_memdup(&curve25519_onion_key,
                                sizeof(curve25519_keypair_t)));
   }
-  if (!tor_mem_is_zero((const char*)
-                          last_curve25519_onion_key.pubkey.public_key,
-                       CURVE25519_PUBKEY_LEN)) {
-    dimap_add_entry(&m,
-                    last_curve25519_onion_key.pubkey.public_key,
+  if (!tor_mem_is_zero((const char*)last_pk, CURVE25519_PUBKEY_LEN)) {
+    dimap_add_entry(&m, last_pk,
                     tor_memdup(&last_curve25519_onion_key,
                                sizeof(curve25519_keypair_t)));
   }