Do not sort twice when changing role and order at the same time

Summary:
When using the list header to change the role and order, if one
changes the order to descending and then changes role, dolphin
also changes the order back to ascending. This results in sorting
the list of files twice in a row. This patch removes the first
(useless) sort.

Reviewers: #dolphin, elvisangelaccio

Reviewed By: #dolphin, elvisangelaccio

Subscribers: elvisangelaccio, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D17111