Don't send a registration email when we invite already existent users by email

[maxceem]

This issue was already fixed in several commits like this one fa2fd52 and few next commits for small issues.

And after the fixes, I couldn't reproduce this issue anymore. But now I can reproduce it again.

For example, I'm inviting by email existent user to this project https://connect.topcoder-dev.com/projects/7709

I got register emails for both emails:

fyi @RishiRajSahu

[maxceem]

Ok, I think it's not an issue. The reason why I got registration email for my user was that before I've tested changing email with this user.
I've requested changing email but I didn't finish the process. When I request changing email my account become inactive but I didn't confirm changing email, instead, I've just reactivated my user using admin panel.

This led to the fact that identity service returns "undefined" instead of the email for this user, see #235 (comment).

I'm closing this issue as it works after fixing data for my user in the identity service.

fyi @RishiRajSahu