When Username is correct and Password is not in sign in form, username should not be cleared

Preconditions: log out from Antarcticle

1. Go to Antarcticle main page
2. Click on Sign in link in right top corner of the page
3. Enter valid Username
4. Leave Password field blank
5. Press Sign in button

AR: Username and password are cleared; Error message: "Incorrect Username or Password!"
ER: Username is still be written in username field in red color ; Error message that password is incorrect