Fix for "Can't place cursor after combining accent"

This patch fixes behavior where attempting to place the cursor at
the end of a string where the last character is a combining accent
actually placed it before that accent. This was especially annoying
for editing Thai text, because it made it difficult to delete a
trailing tone mark.

Fixes bug 8947569 "Can't place cursor after combining accent" and bug
10398332 "[Thailand] Thai Language(IME) -- Can't delete Thai tone mark
while writing message"

Change-Id: Ida1933c8f0ab6cdb0200db39891e9389e4bdba86