[OMPT] implicit task end might be called early

[jprotze]

#pragma omp parallel num_threads(2)
#pragma omp master
{
#pragma omp task
{}
sleep(1);
}

The worker thread has the chance to reach the final barrier before the master thread initialized the taskteam -> the worker thread calls ompt-implicit-task-end and might still execute the generated task.

kmp_wait_release.h:271 should not check for this_thr->th.th_task_team == NULL