allpaths.c:find_join_paths(): compute_rel_size() shouldn't be called

for join-relations. Sizes already computed by
prune_rel_paths():compute_joinrel_size().

joinrels.c:
<                   if ( _use_right_sided_plans_ )
---
>                   if ( _use_right_sided_plans_ &&
>                               length (outer_rel->relids) > 1 )

 - r_plans are useful when outer_rel is join-relation... It
decreases the size of search space...