cryptsetup: do not print (null) if pkcs11 uri not set

The pkcs11 uri is no set if the smart card is not inserted while using
`pkcs11-uri=auto` with libcryptsetup plugins.

```
> systemd-cryptsetup attach cr_data /dev/sda1 - pkcs11-uri=auto
Set cipher aes, mode xts-plain64, key size 512 bits for device /dev/sda1.
Security token (null) not present for unlocking volume Linux filesystem (cr_data), please plug it in.
```

src/cryptsetup/cryptsetup.c

@@ -1503,8 +1503,8 @@ static int attach_luks_or_plain_or_bitlk_by_pkcs11(
                         if (r < 0)
                                 return r;
 
-                        log_notice("Security token %s not present for unlocking volume %s, please plug it in.",
-                                   uri, friendly);
+                        log_notice("Security token%s%s not present for unlocking volume %s, please plug it in.",
+                                   uri ? " " : "", strempty(uri), friendly);
 
                         /* Let's immediately rescan in case the token appeared in the time we needed
                          * to create and configure the monitor */