MB-9738: Fix quick bucket deletion after recreate

Reset curWorkers to 0 when the last bucket disappears
so that the next set does not result in blocked
threads

Change-Id: I73bb8936be01beaac606c49b75982478e414f94c
Reviewed-on: http://review.couchbase.org/31306
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>