aklog: Fix buffer overflows in next_path

Use strlcpy and strlcat

Caught by coverity (#985765)

Reviewed-on: http://gerrit.openafs.org/9447
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit f4373e7867abd50b3fe39716073811794fe62379)

Change-Id: I45d3be18e2975443ce2135f4057128e51d995fa2
Reviewed-on: http://gerrit.openafs.org/11061
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>