trash: Fix directorysizes cache parsing

Summary:
Entries in this file have the following format:
[size] [mtime] [percent-encoded-directory-name]
, and TrashSizeCache::add() writes them correctly,
but TrashSizeCache::calculateSize() reads [mtime]
as [size] and vice versa.

Reviewers: Frameworks, dfaure

Reviewed By: dfaure

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D15317