some char candidate is not visible when near the bottom of screen

Created by: dictcp

Summary When I am typing Chinese in gedit (other any other text editor/textarea), part of the ibus char selection window is not visible when the windows is too long (in term of height).

Package versions: ubuntu 16.04.1 ibus-cangjie-2.4-1

Steps to reproduce:

1. install ubuntu, ibus-cangjie and gedit
2. enable quick input method
3. move the window to the bottom edge of the screen
4. try typing in the address bar
5. partial of the char selection windows was not in the visable screen

Expected behavior: the entire windows should be visible

Reproducible Always