liblog: logprint: report truncated event log contents if error

We need to accept that a log tag can contain no payload.  For those
that are corrupted, and to aid debugging, report what we did manage
to interpret.  Report last character as a ! for corruption, and ^
for truncation.  Fix a few Android Coding standard issues.

Test: gTest logcat-unit-tests
Bug: 32903864
Change-Id: Id11bef3a7b6569305c51701dd66c45d2038d6628