some index join path result collection can be simplied.

## Enhancement

for index join path result, when the result is nil, we can just continue as a short cut, rather than step into compare function.

and for the second pic, since index join paths could be that much for TP heavy workload, and index join probe target only care about the index whose index columns cover the inner join keys. maybe we could make it fast rather than every time step into the compare func.