fixed crash when searching via Find Text bar

Introduced with b41332475783c31136673fb44cf4c411bb0148f8
Integrate branch of IAccessible2

Find Text bar is not the search dialog, so there is no child window
unless the Find & Replace dialog is also open.

Change-Id: Ice230cb2c05534c754fefc55bb8d8b189724d328
maybe better guard against a NULL child window also here

Change-Id: Iad65806894df2454e4341a49f473c308d47660eb
const as const can

Change-Id: I0610bdee35fb7a36a183a5617115f3277af8e6a8