[SSSD] [sssd PR#5646][opened] responder: fix covscan issues

[ikerexxe]

   URL: https://github.com/SSSD/sssd/pull/5646
Author: ikerexxe
 Title: #5646: responder: fix covscan issues
Action: opened

PR body:
"""
Fix two covscan issues that I accidentally included in commit
f890fc4b592767f3f0b2bd5515cbd9516505ebe9.

Error: FORWARD_NULL (CWE-476): [#def60]
sssd-2.4.0/src/responder/common/responder_common.c:1009: var_compare_op: Comparing
"rctx->sock_name" to null implies that "rctx->sock_name" might
be null.
sssd-2.4.0/src/responder/common/responder_common.c:1039: var_deref_model: Passing null
pointer "rctx->sock_name" to "strlen", which dereferences it.

Error: CLANG_WARNING: [#def61]
sssd-2.4.0/src/responder/common/responder_common.c:1039:64:
warning[core.NonNullParamChecker]: Null pointer passed to 1st parameter expecting
'nonnull'

Resolves: https://github.com/SSSD/sssd/issues/5638
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/5646/head:pr5646
git checkout pr5646