incorrect handling of empty email field on login page

[CarlosZBent]

If the user attempts lo log in using an email but not a password, the validation works and it show an error saying "You must provide both email and password." But if both email and password are missing, the validation fails and it shows this in dev mode:

and this in prod (while not showing any error on screen):

[hrydgard]

Will actually deploy the fix tomorrow.