kdb: don't dereference a null pointer on corrupt database

kdb: don't dereference a null pointer on corrupt database

When iterating through the database, kdb would dereference a
null pointer if it encountered an error retrieving the value
or if the value was not the right length, in code that was clearly
cut-and-pasted from the other branch of an "if" statement where a
specific entry was requested on the command line.  Print the name
of the entry with the problem as was apparently intended.

Found-by: clang static analyzer
Reviewed-on: http://gerrit.openafs.org/5174
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit ae6a3929489035ddcd17785abab8900cebd22eb3)

Change-Id: I5c79189f82a636b923c074d3c69cb3b6fef732aa
Reviewed-on: http://gerrit.openafs.org/5188
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>