Don't overwrite valid node's info

Bugfix on 0.3.4.1-alpha (regression caused by ticket 23873, c2fa7438)

diff --git a/src/feature/nodelist/nodelist.c b/src/feature/nodelist/nodelist.c
index bbaa51a..60eaeb3 100644
--- a/src/feature/nodelist/nodelist.c
+++ b/src/feature/nodelist/nodelist.c
@@ -1821,6 +1821,7 @@ node_ipv6_or_preferred(const node_t *node)
     if (r && tor_addr_port_is_valid(&(r)->ipv4_addr, (r)->port_field, 0)) { \
       tor_addr_copy(&(ap_out)->addr, &(r)->ipv4_addr);                      \
       (ap_out)->port = (r)->port_field;                                     \
+      return;                                                               \
     }                                                                       \
   STMT_END