get_to_be_filtered_caps not checking for $obj

[irondan]

Moved to version 3.6.1 (from version 3.5.x) this month and the number of warnings I started seeing on my site reported by sentry.io skyrocketed (somewhere like 130k more than average in the last 24 hours). They all have been stemming from the get_to_be_filtered_caps function in class_coauthors_plus.php. Specifically, once it enters the loop it's not checking that $obj or $obj->cap is not null before accessing properties on it.

Warning: Attempt to read property "cap" on null

Right now I'm just documenting the issue with this ticket; I've not investigated the root cause so feel free to update this ticket as needed.