The field provisioning code generates a randum number to use as the
device id, and then restricts the data to alphanumeric characters.
Previously, it could have also included a 0 byte in the data. This CL
corrects that.
bug: 9073146
Merge of https://widevine-internal-review.googlesource.com/#/c/5740/
from the Widevine CDM repository
Change-Id: Iaf3e9e733f7c66c19d4168178a8e25ee0ba7e936