Remove comparing username to NULL in tls_lock_username

Remove comparing username to NULL in tls_lock_username

tls_lock_username is only called in a single place and that place
calls this is function with up->username, which is always defined.

Change-Id: Ib8adf7b31cae02e2de3d45da23b76a2d79f13e20
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20250121161247.37883-1-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg30520.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>