libutils: fix overflow in String8::allocFromUTF8 Patch contributed in: https://code.google.com/p/android/issues/detail?id=182908 Bug: 23290056 (cherry picked from commit 4eeacbeec0ae66e9d9395abbf83666709f2e11e3) Change-Id: Ife1dc0791040150132bea6884f1e6c8d31972d1b (cherry picked from commit ebabef275283f771151ec93c17469374b789b2c8)