Bug#670412: geli init script fails if /etc/default/geli is unconfigured

[Stefan Bühler <stbuehler@lighttpd.net>]

Package: geom
Version: 9.0+ds1-3

The geli init script fails if no geli devices are configured in 
/etc/fstab and /etc/default/geli.
This prevented an upgrade of geom and freebsd-geom:

[...]
Setting up geom (9.0+ds1-3) ...
Starting GELI subsystem...UNCONFIGURED. See /etc/default/geli ... failed!
invoke-rc.d: initscript geli, action "start" failed.
dpkg: error processing geom (--configure):
 subprocess installed post-installation script returned error exit status 1
configured to not write apport reports
                                      dpkg: dependency problems prevent 
configuration of freebsd-geom:
 freebsd-geom depends on geom; however:
  Package geom is not configured yet.
dpkg: error processing freebsd-geom (--configure):
 dependency problems - leaving unconfigured
[...]

As geom contains more than just geli it is imho wrong to print an error 
(warning is fine ofc), but it certainly is wrong to fail the init script.