Merged in masayuki2009/nuttx.nuttx/lc823450 (pull request #524)

Fix DEBUGASSERT() issues with nxhello on lc823450-xgevk

* sched/task: Remove DEBUGASSERT in task_exitstatus() and task_groupexit()

* graphics: Change DEBUGASSERT condition in nx_runinstance()

Approved-by: Gregory Nutt <gnutt@nuttx.org>