bin: Consistently handle invalid configuration in update
bin: Consistently handle invalid configuration in update

Consistently handle invalid database configuration by reporting the
error and continuing with remaining databases. Functional changes from
previous version:

* When loading key-file fails: no change.
* When group name is invalid: used to be ignored.
* When key name is invalid: used to fail on an assertion.
* When value is invalid: no change.

GNOME/dconf,GNOME/dconf,GNOME/dconf,GNOME/dconf