Avoid unnecessary object allocation in CryptoInfo.set

This is causing a large number of unnecessary small object allocations
during encrypted playbacks, which presumably all need to be GC'd.

I wasn't sure whether the zero pattern should be static; that might
be objectionable in the platform (unsure?), since it would live
forever from the point of the class being classloaded. It doesn't
make much/any difference in practice in any case.

Test: Safe refactoring CL.
Change-Id: I9ee5fe284b0f854d672d83b97fc51116b0416f91