Fix integer overflow in utf{16,32}_to_utf8_length am: c17624db31 am: 3065de2c86  -s ours am: c282fe5c2c  -s ours am: 47dfd5afee  -s ours am: fc4b272afe  -s ours am: 069ec60f20  -s ours am: 3c374a2ba7  -s ours am: cee1faef67  -s ours am: 8ecef89ed0  -s ours am: 78a6b7e28c  -s ours am: 3560e92125  -s ours
am: 173087ab08  -s ours

Change-Id: Ic3204d08df1ec43c937734adb24bf0a28f5f03e9