When calculate_cond_selectivity_for_table() takes into account multi-
column selectivities from range access, it tries to take-into account
that selectivity for some columns may have been already taken into account.
For example, for range access on IDX1 using {kp1, kp2}, the selectivity
of restrictions on "kp2" might have already been taken into account
to some extent.
So, the code tries to "discount" that using rec_per_key[] estimates.
This seems to be wrong and unreliable: the "discounting" may produce a
rselectivity_multiplier number that hints that the overall selectivity
of range access on IDX1 was greater than 1.
Do a conservative fix: if we arrive at conclusion that selectivity of
range access on condition in IDX1 >1.0, clip it down to 1.
