Ensure appended emails have a comma separator

There was some code that checked for comma placement, but that is no
longer necessary. Instead, we verify that the email address has a
trailing comma (plus optional whitespace), and if not, we append a
comma and space, to ensure the address is later chipified correctly.

Bug: 8272316
Change-Id: Ifbb1bae466e3ae15c39d6b90a4bc22edc72a096f