[BUG] dynamic connection throttling could return a max of zero conns

[BUG] dynamic connection throttling could return a max of zero conns

srv_dynamic_maxconn() is clearly documented as returning at least 1
possible connection under throttling. But the computation was wrong,
the minimum 1 was divided and got lost in case of very low maxconns.

Apply the MAX(1, max) before returning the result in order to ensure
that a newly appeared server will get some traffic.
(cherry picked from commit 819970098f134453c0934047b3bd3440b0996b55)