Editor crash with Japanese ATOK input(candidate list related)

This is probably a continuation from [Link Removed].
[Link Removed] fixed the crash with MS-IME input, but crash/instability can still happen with another Japanese input system, ATOK.

0. Make sure you are using ATOK as Japanese input.
1. Create a default level if there is none
2. Tweak the layout to make the details panel height shorter
3. Select PlayerStart
4. Start inputting some Japanese in Player Start Tag and display the candidate list
5. While the candidate list is displayed, scroll the detail panel to make the Player Start Tag outside the view
6. Click on other viewport or menu to see editor crash