LDEV-4293 Skip isSysAdmin check when there is no session
The code that checks if user is sysadmin depends on HTTP session being
present in SessionManager. It is normally present as the authentication
request goes through SsoHandler which initiates the session. It is not
the case, though, when session gets replicated and UniversalLoginModule
is accessed directly.
The fix skips the check in no session is present, which means that
sysadmin will need to authenticate same as regular user, which is OK for
this edge situation. Session failover still works.
