Fix assert in ThreadPool::wait_or_work (#1867)
Fix assert in ThreadPool::wait_or_work (#1867)

Before executing `inner_task`, we intend to assert that it is valid. However,
we are incorrectly asserting that the outer `task` is valid.

Co-authored-by: Joe Maley <16a9a54ddf4259952e3c118c763138e83693d7fd@tiledb.com>
TileDB-Inc/TileDB,TileDB-Inc/TileDB,TileDB-Inc/TileDB,TileDB-Inc/TileDB