[SSSD] [PATCH] Two code-hardening patches

[Jakub Hrozek]

Hi,

these two patches add error handling to the code. The first prevents
operating on ldb_message if retrieving the message fails. I only tested
an SSH login with a UPN to make sure we actually hit this codepath. I
don't like the deep indendation nesting, so I welcome suggestions how to
fix the code better.

The second just checks a return value.