can't delete activity where user_id is empty

[magnus78]

Deleting activity where user_id is empty is prohibited. This can e.g. be group activities imported from external feeds.

Works fine when i remove the empty check.

[magnus78]

proposed fix

[boonebgorges]

It's fine to remove the user id check as suggested in the patch, but then we need to modify bp_activity_user_can_delete() to make sure it doesn't return true for logged-out users (logged-in user id = 0).

[DJPaul]

This patch needs updating per boonebgorges' feedback in order for 1.7.

[boonebgorges]

(In [6732]) Allow activity items to be deleted when the user_id key is empty

Some plugins create activity items that are not attached to a specific user_id.
The activity deletion request handlers (AJAX and bp-activity-actions) prevent
deletion of activity items when the item's user_id value is empty. This
changeset moves this security measure to the bp_activity_user_can_delete()
function, so that anonymous activity items can still be deleted by item admins.

Props magnus78

Fixes #4735

Trac ticket: ​https://buddypress.trac.wordpress.org/ticket/4735

The tests will fail here since the final version of the code is still under development and I didn't apply the latest here.

Closing pr since the code was bunbled into the original patch.