Ton of notices in activity stream for type user_registered

[slaFFik]

I experimented with users registrations. While doing this I was not deleting user properly - using wp-admin area, but just deleting rows in wp_users and wp_usermeta. Each time the user was registered a new activity was recorded. I didn't clean them up.

After this on activity stream I see a lot of notices - activity item itself referencing a user by user_id that doesn't exist in the system and without checks tries to use user's data.

Notice: Undefined property: stdClass::$user_nicename in \wp-content\plugins\buddypress\bp-activity\bp-activity-template.php on line 1144

Notice: Undefined Property: Stdclass::$user_login in \wp-content\plugins\buddypress\bp-activity\bp-activity-template.php On Line 1144

I guess these properties should be checked before their use in the code.

[boonebgorges]

In 8477:

Check user properties before attempting to use in bp_get_activity_user_link()

This prevents PHP notices when users have been incompletely deleted from the DB.

Fixes #5685