Avoid giving an stderr to kwallet

Summary:
The fixes for CVE-2018-10380 introduced a regression for most users not
using kde, and some for kde sessions. In particular the reorder of the
close calls and creating a new socket caused that the socket is always
assigned the file descriptor 2, aka stderr.

BUG: 393856

Test Plan: It works

Reviewers: #plasma, aacid

Reviewed By: aacid

Subscribers: asturmlechner, rdieter, davidedmundson, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D12702