Fix a memory leak when adding an ri with expired ed certs

Fixes bug 16539; bugfix on 0.2.7.2-alpha.

changes/bug16539

@@ -0,0 +1,4 @@
+  o Minor bugfixes (Ed25519):
+    - Fix a memory leak when reading router descriptors with
+      expired Ed25519 certificate. Fixes bug 16539; bugfix on 0.2.7.2-alpha.
+      

src/or/routerlist.c

@@ -3295,6 +3295,8 @@ router_add_to_routerlist(routerinfo_t *router, const char **msg,
 
   /* Make sure that it isn't expired. */
   if (router->cert_expiration_time < approx_time()) {
+    routerinfo_free(router);
+    *msg = "Some certs on this router are expired.";
     return ROUTER_CERTS_EXPIRED;
   }