bus-message-util: initialize variables to make gcc happy

gcc 13 on armhf complains with -Wmaybe-uninitialized about family, port
and server_name in bus_message_read_dns_array(), even though they are
always set when bus_message_read_dns_one() returns > 0.

(cherry picked from commit da4052d0037c6bb4981387bb375355f595ab4b1c)

src/shared/bus-message-util.c

@@ -184,10 +184,10 @@ int bus_message_read_dns_servers(
                 return r;
 
         for (;;) {
-                const char *server_name;
+                const char *server_name = NULL; /* avoid false maybe-uninitialized warning */
                 union in_addr_union a;
-                uint16_t port;
-                int family;
+                uint16_t port = 0;              /* avoid false maybe-uninitialized warning */
+                int family = AF_UNSPEC;         /* avoid false maybe-uninitialized warning */
 
                 r = bus_message_read_dns_one(message, reterr_error, extended, &family, &a, &port, &server_name);
                 if (r < 0)