AT COST_MODEL_SERVER::TMPTABLE_READWRITE_COST()

Problem:
While calculating the cost for doing semjoin_dupsweedout strategy
inner_fnout is calculated wrongly when max_outer_fanout becomes 0.
This causes mysql server to exit later.

Solution:
Calculate the inner_fanout only when max_outer_fanout is > 0. Else
there is no need to recalculate inner_fanout w.r.t max_outer_fanout.