exit with nonzero status if certificate expiration dump fails

Fixes bug 23488.

Bugfix on b2a7e8df900eabe41d6e866f; bug not in any released Tor.

src/or/main.c

@@ -3785,7 +3785,6 @@ tor_main(int argc, char *argv[])
   case CMD_KEY_EXPIRATION:
     init_keys();
     result = log_cert_expiration();
-    result = 0;
     break;
   case CMD_LIST_FINGERPRINT:
     result = do_list_fingerprint();