Bug 10735: prevent koha-dump from aborting if backupdir undefined

Bug 10735: prevent koha-dump from aborting if backupdir undefined

Older versions of Koha didn't have <backupdir>...</backupdir> defined in
koha-conf.xml. The koha-dump script is aware of this, and checks to see
if it's there. However, if it's not, xmlstarlet returns a non-0 error
code which causes the script to abort due to running under set -e.

Test plan:
 * Remove backupdir from koha-conf.xml
 * Run koha-dump, notice that it doesn't do backups
 * Apply patch
 * Run koha-dump again, notice that it does do backups

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>
The fallback method works as described. It might be made more robust
like checking for dir existence (thinking of older instances upgrades).
But it certainly belongs to another bug report.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
As Tomas said, it would be better to alert the user if the backupdir tag
does not exist (or contains a nonexistent directory) in the config file.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit 266f2a3a9f3d67fed0e0b35d267419a901345b92)
Signed-off-by: Fridolin SOMERS <fridolin.somers@biblibre.com>