core: Fix translations of --help
* src/argparse.c (show_help): Do not translate the empty string.
PO files use the empty string for meta information. However, to mark
the end of the heder group we also use an empty string and that one
gets translated - boom. Example of this error:
[...] -u, --local-user USER-ID [...] Project-Id-Version: gnupg-2.3.0 Report-Msgid-Bugs-To: translations@gnupg.org PO-Revision-Date: 2022-10-07 09:52+0200 Last-Translator: Werner Koch <wk@gnupg.org> Language-Team: German <de@li.org> Language: de MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Plural-Forms: nplurals=2; plural=n != 1; : (Auf der "man"-Seite ist eine volls[...]