logd: klogd crash (part deux)

(cherry pick from commit 83b24789)

LogBuffer::pidToUid(pid_t pid) { return stats.pidToUid(pid); }
needs to have LogBuffer::lock()/unlock() to prevent unordered_map
data corruption. This can lead to multiple symptoms, crashes and
continuous spins on corrupted iterators.

Bug: 30688716
Bug: 30050636
Bug: 30614675
Bug: 25620123
Bug: 30792935
Change-Id: I1d8fec8e5fda98c6a08645e7456b081507696b3c