_node_query_node_access_alter excludes results with missing relations

Steps to reproduce:

- Enable content access (any module implementing hook_node_grants should work)
- Enable views and entity-reference modules
- Create two content types, let the first one reference the other through a entity-reference field
- Create some content of the first content type, but don't bother adding any relations
- Create a view with a relation through an entity-reference, don't mark this relation as required (LEFT JOIN)

Without the 'bybass node access' privilege, users will not get any results in this view.

It's easier to illustrate with an example.

Something like could for example be appended to the node query:

... AND ( EXISTS  (SELECT na.nid AS nid
FROM 
node_access na
WHERE (( (na.gid = '0') AND (na.realm = 'all') )OR( (na.gid = '0') AND (na.realm = 'content_access_author') )OR( (na.gid = '1') AND (na.realm = 'content_access_rid') ))AND (na.grant_view >= '1') AND( node_field_data_field_person.nid = na.nid))

where node_field_data_field_person is the referenced base table of a "person" content type referenced through an entity-refrence field. node_field_data_field_person.nid will in the case where no such relation exists be NULL (because of the LEFT JOIN from the node table). This will cause the EXISTS condition to evaluate to FALSE, and the row to be excluded.

To remedy this the query should be written like this to protect against the case where node_field_data_field_person.nid IS NULL.

... AND ( EXISTS  (SELECT na.nid AS nid
FROM 
node_access na
WHERE (( (na.gid = '0') AND (na.realm = 'all') )OR( (na.gid = '0') AND (na.realm = 'content_access_author') )OR( (na.gid = '1') AND (na.realm = 'content_access_rid') ))AND (na.grant_view >= '1') AND( (node_field_data_field_person.nid IS NULL ) OR (node_field_data_field_person.nid = na.nid) )))

I will attach a patch with the needed changes.