Ensure that codestyle.py always returns something on stdout to unlock m_mutex.

Authored by fviard on Mar 20 2018, 12:03 AM.

Description

Ensure that codestyle.py always returns something on stdout to unlock m_mutex.

By returning only a "0" size on stdout, pythonstylechecking.cpp will
see a "reply" and unlock the m_mutex.

This avoids serious UI hangs when the stylechecker is enabled but
pycodestyle is not installed.

BUG: 392031
Differential Revision: https://phabricator.kde.org/D11474