Bug 13285 Do the right thing if opacthemes is not set

Bug 13285 Do the right thing if opacthemes is not set

If opacthemes is not defined updatedatabase reports the
subsequent warnings as an error. Take account of the case where
it is not set and default that to bootstrap.

This is probably a rare occurence, but should be handled

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
(cherry picked from commit 90c32e88561530143ced5d190445850291f6851e)
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>