[TreeTableView] Focus is lost during selection with SHIFT + UP/DOWN

To reproduce expand root and push buttons: "Enable multiple selection", "Enable cell selection".
1. After that click on the first cell and push SHIFT + DOWN. Two cells will be selected.
Then push SHIFT + UP two times. You will see that the focus will be lost.

2. Click on the first cell. Push SHIFT + DOWN until all the cells become selected.
Then push SHIFT + DOWN once again. The focus will be lost.