it fixes xgettext and (maybe) friends

[12:22:29] Error: Command failed: misc/translator/xgettext.pl --charset=UTF-8 -s -o /tmp/koha-Jaa9rf/Koha-marc-NORMARC.pot -f /tmp/koha-Jaa9rf/files
/tmp/koha-Jaa9rf/Koha-marc-NORMARC.pot at misc/translator/xgettext.pl line 387.
Use of uninitialized value in subroutine entry at misc/translator/xgettext.pl line 388.
Argument ">:encoding(utf-8)" isn't numeric in subroutine entry at misc/translator/xgettext.pl line 388.
Argument "/tmp/koha-Jaa9rf/Koha-marc-NORMARC.pot" isn't numeric in subroutine entry at misc/translator/xgettext.pl line 388.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>