sd-bus: free everything when bus_set_address_user fails (systemd#6552)

Fixes:
```
$ env -i valgrind --leak-check=full ./build/test-bus-chat
...
==7763== 1,888 (1,824 direct, 64 indirect) bytes in 1 blocks are
definitely lost in loss record 2 of 2
==7763==    at 0x4C2FA50: calloc (vg_replace_malloc.c:711)
==7763==    by 0x4F8FF9A: sd_bus_new (sd-bus.c:175)
==7763==    by 0x4F938BF: sd_bus_open_user (sd-bus.c:1138)
==7763==    by 0x109ACD: server_init (test-bus-chat.c:70)
==7763==    by 0x10BCF8: main (test-bus-chat.c:526)
==7763==
```

Closes systemd#6481

Author: evverx

src/libsystemd/sd-bus/sd-bus.c

@@ -1141,7 +1141,7 @@ _public_ int sd_bus_open_user(sd_bus **ret) {
 
         r = bus_set_address_user(b);
         if (r < 0)
-                return r;
+                goto fail;
 
         b->bus_client = true;
         b->is_user = true;