ubik/udebug.c, vol/vol-info.c: check array index before dereferencing

ubik/udebug.c, vol/vol-info.c: check array index before dereferencing

Avoid out-of-bounds array accesses by first checking that the index
is in-bounds, and then dereferencing; not the other way around.

Change-Id: Ib36a28ca6181a7a7fd602de45cb5a15fad099a44
Reviewed-on: http://gerrit.openafs.org/8879
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>