[tabswitcher] Fix beginRemoveRows call
Summary:
To remove one row first and last should be the same index.
This hit an assert on newer Qt.
Test Plan:
I hit this booting up with no args with kate
restoring to split views each with one document.
From the calling code it seems to be trying to just remove one row.
It now starts. Hitting control+n, control_w does add/remove tabs respectively
Reviewers: Kate, dhaumann
Reviewed By: Kate, dhaumann
Subscribers: dhaumann, kwrite-devel
Tags: Kate
Differential Revision: https://phabricator.kde.org/D16376