sched/sched_releasetcb.c: Fix an error handling case where a pthread start-up...

sched/sched_releasetcb.c:  Fix an error handling case where a pthread start-up fails early, before the task type has been saved in the TCB.  It is safer to use the sched_releasetcb() task type argument instead of relying on the task type in the TCB to be valid.  Reported by David Sidrane