Fix integer overflow in utf{16,32}_to_utf8_length am: c17624db am:...

Fix integer overflow in utf{16,32}_to_utf8_length am: c17624db am: 3065de2c  -s ours am: c282fe5c  -s ours am: 47dfd5af  -s ours am: fc4b272a  -s ours am: 069ec60f  -s ours am: 3c374a2b  -s ours
am: cee1faef  -s ours

Change-Id: I98ed8072c558f9ebbd402972ee4c22d246f094b9