Submitting form with subscribed email returns error

[marcoelho97]

Hello,

Just noticed that when submitting the form with an email that's already subscribed, it returns an error instead of a warning.

No errors in the backend of OctoberCMS.

[LukeTowers]

@marcoelho97 feel free to submit a PR to change this, although I would suggest that this is desired behaviour because otherwise a bad actor could use the error message to determine whether or not given emails were signed up to specific lists already.