Fix maximize Apply Now rule

Summary:
AbstractClient applies maximize rules by running

    maximize(maximizeMode());

but because window rules are checked only in changeMaximize
implementation, the if statement prevents us from applying maximize
rules (m and maximizeMode() are equal).

Reviewers: #kwin, romangg

Reviewed By: #kwin, romangg

Subscribers: romangg, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D22255