Fix more of the same crash

Author: jbkempf

src/mdns.c

@@ -117,7 +117,9 @@ mdns_list_interfaces(multicast_if** pp_intfs, size_t* p_nb_intf, int ai_family)
                 return (MDNS_ERROR);
         }
         for (c = ifs; c != NULL; c = c->ifa_next) {
-                if (c->ifa_addr->sa_family != ai_family || !mdns_is_interface_valuable(c))
+                if (c->ifa_addr == NULL ||
+                    c->ifa_addr->sa_family != ai_family ||
+                    !mdns_is_interface_valuable(c))
                         continue;
                 memcpy(intfs, c->ifa_addr, sizeof(*intfs));
                 intfs++;