Optimize Query jumble

Optimize Query jumble

f31aad9b0 adjusted query jumbling so it no longer ignores NULL nodes
during the jumble.  This added some overhead.  Here we tune a few
things to make jumbling faster again.  This makes jumbling perform
similar or even slightly faster than prior to that change.

Author: David Rowley <[email protected]>
Reviewed-by: Michael Paquier <[email protected]>
Discussion: https://postgr.es/m/CAApHDvreP04nhTKuYsPw0F-YN+4nr4f=L72SPeFb81jfv+2c7w@mail.gmail.com