Fix Null pointer dereference in the spawnd daemon.
Fix Null pointer dereference in the spawnd daemon.

External symptoms: crash during call of the spawn_wait_coreid() called with
the domain id of already closed domain.

Signed-off-by: Gerd Zellweger <1d6e1cf70ec6f9ab28d3ea4b27a49a77654d370e@gerdzellweger.com>

8l/barrelfish,kishoredbn/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,8l/barrelfish,BarrelfishOS/barrelfish,8l/barrelfish,8l/barrelfish,8l/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,BarrelfishOS/barrelfish,kishoredbn/barrelfish,8l/barrelfish