[FIX] m.ComboBox: fix flickering issue when F4 or Alt + DOWN are pressed

- to prevent flickering, the filter is cleared after the close
animation is completed

Change-Id: I2fdce97a477d7692b9dcf82efeced7c769983e32
Merge "[FIX] m.ComboBox: fix flickering issue when F4 or Alt + DOWN are pressed"