Missing followed user's actions in the live notifications email

Steps to reproduce:

• in xwiki.properties, set `notifications.emails.live.graceTime = 1`
• as UserA, set a valid email (just like in XWIKI-15034)
• as UserA, go to the notification preferences
• disable all notifications
• set email interval to "LIVE"
• then go to the profile of UserB
• mark her as followed
• log as UserB, perform some actions (add a comment on a page for example)

EXPECTED RESULTS:
1 minute after, an email is received by UserA about the action done by UserB

ACTUAL RESULTS:
No email is received.

The cause of this problem is described there: https://github.com/xwiki/xwiki-platform/commit/7b67d9747932e244718dff6f13eed9ae5302fd6d