sql: bugfix: early return in joinerbase.render
sql: bugfix: early return in joinerbase.render

This commit modifies joinerbase.render to return no rows when trying to
render a join row with a null side that the current join mode does not
permit.

maxlang/cockroach,glycerine/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,maxlang/cockroach,glycerine/cockroach,maxlang/cockroach,maxlang/cockroach,paperstreet/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,vaibhavarora/cockroach,glycerine/cockroach,vaibhavarora/cockroach,vaibhavarora/cockroach,maxlang/cockroach,paperstreet/cockroach,maxlang/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,glycerine/cockroach,glycerine/cockroach,paperstreet/cockroach,maxlang/cockroach,glycerine/cockroach,paperstreet/cockroach,paperstreet/cockroach,maxlang/cockroach,vaibhavarora/cockroach,glycerine/cockroach,vaibhavarora/cockroach,glycerine/cockroach