Set display_value in krb5_gss_get_name_attribute

Set display_value in krb5_gss_get_name_attribute

A backwards conditional in r25358 caused krb5_gss_get_name_attribute
not to set display_value on success.  Fix the sense of the
conditional.

We still don't quite correctly handle the cases where data_to_gss()
fails, but those should be rare and the problem in those cases isn't
severe, so it can be fixed separately.

Also, value and display_value should probably be initialized to null
buffers on failure, as is common with GSS interfaces.

ticket: 7087
status: open
target_version: 1.10.1
tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@25674 dc483132-0cff-0310-8789-dd5450dbe970