Fix status update (darksend mixing stuck)

Fix darksend mixing stuck on newAccepted == 0 and newStatus == POOL_STATUS_ACCEPTING_ENTRIES - without UpdateState DoAuto... will never pass second if there https://github.com/darkcoin/darkcoin/blob/master/src/darksend.cpp#L1395
```if(state == POOL_STATUS_ERROR || state == POOL_STATUS_SUCCESS) return false;```
because of previously changed state here https://github.com/darkcoin/darkcoin/blob/master/src/darksend.cpp#L1169-L1172
```
        if(newAccepted == 0){
            UpdateState(POOL_STATUS_ERROR);
            lastMessage = error;
        }
```