validateUniqueUsername(), validateUniqueEmail() are called after input validations and each other, so not all validation errors are shown together

steps to reproduce:

• go to /register
• enter a nick and e-mail that's already taken
• leave one required input empty
• submit with register button

expected behaviour

• all validation errors ("nick not unique", "e-mail not unique", "required input empty") are shown together

real behaviour

• only "required input empty" validation error is shown
• after entering the missing input and submitting with "register" button only "nick not unique" validation error is shown
• finally after changing the nick to a unique nick, "e-mail not unique" validation error is shown