Transition from DEMAND->NO_DEMAND:
Two concurrent threads enter DEMAND.request and DEMAND.onDataAvailable.
And DEMAND.onDataAvailable finishes before DEMAND.request to be able to
update the demand field then a request for reading will be lost.
Transition from READING->NO_DEMAND:
readAndPublish() returns false because there is no demand but before
switching the states READING.request is invoked again a request for
reading will be lost.
Changing READING->DEMAND/NO_DEMAND is made conditional so that the
operations will be executed only if changing states succeeds.
When in READING state detect completion before each next item in order
to exit sooner, if completed.
Issue: SPR-16207
2a481c5411