When committing a span after a revert, the offset logic was such that it
split a surrogate unicode pair used to express an emoji.
Checking the last character of the span lets us avoid this problem.
Fix for bug 19255233.
Change-Id: I07d18d9002b5075f7925319dd05962011656c311
Dan Zivkovic
Tadashi G. Takaoka
Jean Chalard