core: allow services stuck in reloading state to exit

If a service is in reloading state but has exited do not delay
the final exit until the service reload timer expires. Instead allow
the service to exit immediately since we can't expect the service to
ever transition out of reloading state.

For example if a service sent RELOADING=1 but crashed before it could
send READY=1 then it should be restarted if the service had
Restart= configured.

Signed-off-by: Peter Morrow <pemorrow@linux.microsoft.com>
(cherry picked from commit bbe19f68)