ubik: Don't overflow server's addr array

We're checking to see if we've overflowed the array _after_ we've
looked up an element within it - so on the final iteration, we
always read past the end of the array.

Fix this by swapping the order of the tests in the for statemen

Caught by coverity (#985590)

Change-Id: Ibbf0eb88083166f0a23316edf0612e94593c07ce
Reviewed-on: http://gerrit.openafs.org/9326
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>