GetTaskPolicy dereferenced its MaintenancePolicy argument to look at
TaskPolicies, so IsTaskEnabled, GetMaxConcurrent and GetRepeatInterval
all took the admin process down when handed a nil policy. A nil policy is
not a programming error here: MaintenanceConfig.Policy is unset until
something builds one, DefaultMaintenanceConfig returns a config with no
policy at all, and UpdateConfig installs whatever config it is given.
Found by calling IsTaskEnabled with the policy from a freshly defaulted
MaintenanceConfig.
Treat a nil policy as "no entry": no task enabled, the safe concurrency
default of 1, and a repeat interval of 0 so callers fall back to their
own default instead of reading DefaultRepeatIntervalSeconds off nil.
Also add the startup test this was found with. It walks the admin
server's startup sequence over a data directory that has balance saved as
disabled and checks the state that decides whether issue #10874 happens:
the balance detector reports disabled, vacuum stays enabled, and tasks
whose config was never saved keep their compiled-in default.
Refs #10874
Junker der Provinz
654502ce8f