Fix inconsistency in commit 13f3244 (race condition between editing and saving).

Summary:
Due to a change of heart mid-implementation, the property name set by the view
and the property name checked by the model differed.

And yet all automated tests passed... because they played along with the
two different property names, oops. This confirms to me that proper C++ method
calls checked by the compiler are actually superior than string-based architectures...

Test Plan:
Editing and leaving a trailing space for a few seconds no longer makes
the cursor jump to pos 0.

Due to a new setup I wasn't able to run all automated tests
(cucumber packaging problem in OpenSuSE Leap 42.2; akonadi PayloadExceptions
in many tests). editorviewtest passes though.

Reviewers: ervin

Reviewed By: ervin

Subscribers: Zanshin

Differential Revision: https://phabricator.kde.org/D3698