add comma at the end of input if none is provided

[nicholsk18]

This is more or less a quick fix, but no validation if staff types in two emails without a comma in any of the 3 fields shown here. You can hit send and it will never send to anyone as far as I am aware. To headers are missing and no error anywhere. This adds a comma on space key if it is needed.

[jstanden]

@nicholsk18 Thanks! I can reproduce the issue with space-delimited email addresses in To/Cc/Bcc. I'll review the patch.

In validation, we can probably check the length of the the recipients in each field. If our parsed value is empty we'd also know something went wrong.

[nicholsk18]

Backend would be great to add, but I think for UX it be nice to have something in front end as well