viced: Catch GetCellInfo failure

If GetCellInfo returns a non-zero result, catch the error, rather
than just carrying on regardless.

Caught by clang-analyzer

Change-Id: I6b9ca91c8cea2ff0d68873913abdc0daadcc0e27
Reviewed-on: http://gerrit.openafs.org/9240
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>