daemon: fix DEREF_AFTER_NULL.EX.COND on worker_init (#1467)

Found by the static analyzer Svace (ISP RAS).

After having been compared to a NULL value at worker.c:2216,
pointer 'worker->stat_timer' is passed in call to function
'worker_restart_timer' at worker.c:2319,where it is
dereferenced at worker.c:2029.

Fix that stat_timer creation failure in worker_init does
not continue with a NULL timer that causes a crash later.

Signed-off-by: Petr Vaganov <petrvaganoff@gmail.com>