logd: klogd: parse error

(cherry pick from commit eb298086)

Resolve three areas missing taglen checking. Add some additional
limit-checking paranoia. Problem started when p was allowed to
go beyond the size of the incoming buffer in some blind
p = cp + 1 fragments, placed the check for that after them all
before harm could be done, rather than in each location.

Bug: 25620123
Change-Id: Ib5687fd30ef0cd3ba3bc0df310b436ad675ccabc