[SSSD] [PATCH] sysdb: return proper error code from sysdb_sudo_purge_all

[Jakub Hrozek]

This is the last bug that was reported by clang and not Coverity. Some
of those that clang reported are also reported by Coverity and have
their own tickets (#1330-#1333).

I missed it in the first run because there was the same bug elsewhere in
the same file, I just didn't realize clang was reporting two instances
of the same problem.