ignore first alter call for messageTemplate

Created by: konadave

https://docs.civicrm.org/dev/en/latest/hooks/hook_civicrm_alterMailParams/#:~:text=Note%20that%20this%20hook%20is%20called%20twice%20when%20sending%20a%20message%20template%2C%20once%20early%20in%20the%20message%20generation%20(before%20tokens%20are%20applied%2C%20with%20the%20context%20messageTemplate)%20and%20then%20later%20from%20CRM_Utils_Mail%3A%3Asend()%20with%20the%20context%20singleEmail

I don't know if calling alterMailParams() twice is new behavior, or if the contents for $params has changed when context == messageTemplate. If alterMailParams() runs in this context, it ultimately fails trying to create a mailing event queue without a contact ID, and no message is sent or activities created. Ignoring this context solves the problem.