Fix integer overflow in utf{16,32}_to_utf8_length am: f0a43dede9 am: 33abf90994 am: 789673b15c am: 1436927851 am: d70e582d67 am: 62d5a78df3 am: 5b37a8ce87 am: 16e2001f0b am: e2b5839d4c  -s ours am: 84bdda1e6e  -s ours am: 94222586dc  -s ours am: 16a3ded833  -s ours
am: d9767d6bf0  -s ours

Change-Id: I1a39b43b5311cc9f79a20721601dfb17380c6cf7