ItemSync: skip handling remote items if local changes failed
The infamous "Multiple merge candidates" error would still leave ItemSync
in a forever-stuck state when mRemoteItemsQueue was not empty.
Reproduced by adding a unittest that calls setFullSyncItems (with
a duplicate item), while the existing unittest for a duplicate item
was callling setIncrementalSyncItems().
I barely understand what I'm doing, please review carefully.
Test Plan: Unittest passes.
Reviewers: dvratil, vkrause
Reviewed By: dvratil
Subscribers: asn, kde-pim
Tags: KDE PIM
Differential Revision: https://phabricator.kde.org/D20243