Add bound checks to utf16_to_utf8

FPIIM-590

Bug: 29250543
Change-Id: I3518416e89ed901021970958fb6005fd69129f7c
(cherry picked from commit 1d3f4278b2666d1a145af2f54782c993aa07d1d9)
(cherry picked from commit 0c9742db802c21274fa299fbf7a8bf7c0c49355d)
1 file changed