volinfo: show header filenames even if error

When invoked with -header option, print the header inode
number, and namei filename, even if the header file cannot
be opened.

Reviewed-on: http://gerrit.openafs.org/7190
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Tom Keiser <tkeiser@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit b71f4ffa7c58ef7b27eb6e28d00892906aec49ec)

Change-Id: Ibd68433ea778d5359c873e3764800d60fa7ae95d
Reviewed-on: http://gerrit.openafs.org/11274
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>