Add bound checks to utf16_to_utf8 am: bce11021b2 am: 008120497b am: bab3334226 am: ff58d7c918  -s ours am: 437776ac65 am: 73b29dc307
am: 12128035ae

Change-Id: I9742f3ba3c1aaf1547aee3d0c2ccf1887d7b3f70