Find Participants - Send Email to Contacts: If a contact has multiple selected registrations (different events), send email for each registration

Send Email to Contacts task from Find Participants - if multiple registrations selected for the same contact, we get a notice (see below), AND only one email is sent. We should send an email for each registration (as Tim notes in his comment below).

— Original Post —
When you use the mailing action (mail to participants) on the participant overview a notice appears in a specific situation.

Notice: Undefined offset: 147 in CRM_Contact_Form_Task_EmailCommon::buildQuickForm() (line 229 of /sites/all/modules/civicrm/CRM/Contact/Form/Task/EmailCommon.php).

To reproduce:
-Register contact A for two different events.
-Remove mailadres from contact or mark deceased
-Search participant for different event so contact A shows up in result twice (once for both events).
-Mail to participants (including double participant).

Now the notice shows.
The problem lies inside CRM_Contact_Form_Task_EmailCommon::buildQuickForm(&$form) method. This common class is used in CRM_Event_Form_Task_Email
This method removes the 'deceased / no mailing' contact-ids from the selection before making the form. It howerver removes the first contact-id, before checking the rest. In a participant selection a contact id could however appears twice. Which makes the unsetting done too early. We unset the contact id, and try to iterate through it afterwards.

A solution according to me is split up the buildform method, to get the validation in a seperate method, that way we could override the validation for the participant task.

i'll create a PR.