[SSSD] [sssd PR#458][comment] overrides: fixes for sysdb_invalidate_overrides()

[fidencio]

URL: https://github.com/SSSD/sssd/pull/458
Title: #458: overrides: fixes for sysdb_invalidate_overrides()

fidencio commented:
"""
Manual test went fine and our internal CI passed without issues.

CI: http://vm-031.$%7Babc%7D/logs/job/82/02/summary.html

"""

See the full comment at https://github.com/SSSD/sssd/pull/458#issuecomment-348498386