Improved handling of IS_READ in new call log.

It is not marked "not null" in the system call log and our simulator gives it null data, so handle it more gracefully to be on the safe side.

Also enforce "not null" for IS_READ and NEW in annotated call log as I observed that happening somehow (possibly from older builds though).

TEST=existing
Test: existing
PiperOrigin-RevId: 193271095
Change-Id: I780db20c9d6ea5cf5e1d757def9ea06b492267c1