'taxonomy terms in node' + 'parent taxonomy terms of taxonomy terms in node' relationships can result in WSOD

If we have a View listing nodes that has a 'taxonomy terms in node' relationship and also a 'parent taxonomy terms' over the top of the 'taxonomy terms in node' relationship, it will result in WSOD when attempting to query the DB on nodes that have no taxonomy terms.

Adding a filter to query only nodes with taxonomy terms fixes this... but since this behaviour allows administrators to create Views that will break their site, I thought it might be considered a bug here nevertheless.

Only tested on 6.x-2.9.