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

Change-Id: I2b8d19a8582f8de19332705fc4dcdc3a23fa8da2