task/cgroup: Fix for task binding anomaly

Here's how to reproduce on smd-server with 2 sockets, 6 cores per
socket and 2 threads per core, just run the following command line
3 times in quick succession (all active at the same time):
srun --cpus-per-task=4 -m block sleep 30
What was happening is the first job would be allocated cores 0+1
The second job would be allocated cores 2+3
The thrid job would test use of cores 0-3 then exit because the
 job only needs 4 CPUs. The resulting core binding would include
 NO CPUs. The new logic tests that the core being considered for
 use actually has some resources available to the job before
 updating the counter which is being tested against the needed
 CPU counter.