BUG/MAJOR: checks: don't call set_server_status_* when no LB algo is set

David Touzeau reported that haproxy dies when a server is checked and is
used in a farm with only "option transparent" and no LB algo. This is
because the LB params are NULL, the functions should be checked before
being called.

The same bug is present in 1.4 so this patch must be backported.
3 files changed