Send email to existing users if "Invitee email" is disabled

Patch attached.

I used your code, but I had to rewrite the existing code quite drastically.
1) I move the code for sending email to a separate function. So, we can reuse it
2) We still first check email (invitee_mail field) and then invitee (entity_id field), because normally we add invitation by email.
3) If email is empty and invitee is there then we check settings and send email to the user
4) if email is not empty we again try to load a user by email, as it was before and then we check settings and send email to the user

So, I have improved a bit the code and also covered your case. Also I had to move code to presave hook because we have issue with infinite loop 🐛 Entity save() in hook_ENTITY_TYPE_insert() Fixed

Please check MR and I will include the fix to the next release

Thank you for your contribution

Automatically closed - issue fixed for 2 weeks with no activity.