Changed BulkheadImpl.releasePermit to ensure that it claims a permit when running a task from the pending queue

[nicky9door]

Before this change, releasePermit would check the queue but not modify the permit field. This could eventually result in permits being equal to maxPermits and would erroneously report the bulkhead as being full

This should fix issue #365

[jhalterman]

Thanks @nicky9door !