Search Service: an error condition under permission query optimization mode was introduced in 6.5

[landreev]

During the cleanup and refactoring of the permission query building code in SearchServiceBean, under #10706, one very specific use case/workaround got overwritten.
When the permission query optimization mode is enabled (avoid-expensive-solr-join=true) AND the user has more than 1 active group, the combined query must be built a certain way that's different from what we've been using otherwise.
Unfortunately, this was not caught before/during the 6.5 release - because the combination of the above conditions was needed for the issue to manifest itself.

I have however enabled the optimization on demo, where all the users (including the guest/anonymous user, apparently) are members of multiple groups. So, going forward an issue like this will be caught during the deployment there.

Will be easy to rectify. Jim and I talked about this yesterday, he already has a fix that appears to be working at QDR.