DocumentPrivate: Don't scroll view when add auto-bracket at end of file

Summary:
...when 'Allow scrolling past the end of the document' is set

BUG: 399014

Test Plan:
See https://bugs.kde.org/show_bug.cgi?id=399014

Reviewers: KTextEditor, cullmann

Reviewed By: KTextEditor, cullmann

Subscribers: swestersund, cullmann, dhaumann, kwrite-devel, kde-frameworks-devel, KTextEditor

Tags: Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D17857