madx.sh: requested only unlock

small bug fix:
```
$SixDesk/utilities/bash/mad6t.sh -r -U -d hl13B1_HTBoincDev_QP9
Mon 18/06/18 09:01:43  mad6t.sh requested only unlocking. Exiting...
```

For the moment, seen in ```includingHTBoinc``` branch
