Bug 9940: (follow-up) add language-original to QP search field list

Bug 9940: (follow-up) add language-original to QP search field list

This patch adds language-original to the list of search fields
recognized by QueryParser.

To test:

[1] After doing the tests in the main patch, copy the configuration
    file etc/searchengine/queryparser.yaml into place, turn on the
    UseQueryParser system preference, and verify that searching on
    language-original still works.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit e4912a20f9b6f59fb57955777abd1e62d785a1fd)
Signed-off-by: Fridolin SOMERS <fridolin.somers@biblibre.com>