Consistently format addresses in node_get_address_string

Also, don't write to a buffer with length zero.

src/or/nodelist.c

@@ -863,13 +863,13 @@ node_get_prim_addr_ipv4h(const node_t *node)
 void
 node_get_address_string(const node_t *node, char *buf, size_t len)
 {
-  if (node->ri) {
-    strlcpy(buf, fmt_addr32(node->ri->addr), len);
-  } else if (node->rs) {
+  uint32_t ipv4_addr = node_get_prim_addr_ipv4h(node);
+
+  if (tor_addr_is_valid_ipv4h(ipv4_addr, 0)) {
     tor_addr_t addr;
-    tor_addr_from_ipv4h(&addr, node->rs->addr);
+    tor_addr_from_ipv4h(&addr, ipv4_addr);
     tor_addr_to_str(buf, &addr, len, 0);
-  } else {
+  } else if (len > 0) {
     buf[0] = '\0';
   }
 }