Inviting users with groups field failed when there is an existing user in the list

[techAPJ (Arpit Jalan)]

@tgxworld

An error is thrown when there is an existing user even before the security fix.

That is correct the error was being logged in a notification PM when bulk inviting an existing user, but (before the security fix) the user was indeed added to the specified group via this block of code.

Thanks for the proper fix here!