PIN shouldn't be with native digits

Currently validation is broken on Android with Persian UI

See also: http://developer.android.com/reference/java/util/Locale.html#default_locale

Change-Id: I76ade75b4c0b6c4c221f8cb4420bc6bd3c8167f3
Reviewed-on: https://gerrit.libreoffice.org/7778
Reviewed-by: Andrzej Hunt <andrzej.hunt@collabora.com>
Tested-by: Andrzej Hunt <andrzej.hunt@collabora.com>