Fix null pointer dereference when sending a mail to validate the subscription to a group

Fix this error: PHP Fatal error:  Call to a member function bestEmail() on a non-object

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
Fix broken emails admin page : profile ID != user ID

Fetch User and Profile for each broken address and use these objects instead
of calling Profile::get() with $uid.

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>