l10ntools/source/export.cxx: improve style of code

Change-Id: Ieef44da0ab8f2d33faaf8c32970bb9d33df6750b
Reviewed-on: https://gerrit.libreoffice.org/11318
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>