title: Update incomplete partial pipeline data in session
body: <p>I am using python-social-auth for implementing a passwordless authentication flow. Users submit their e-mail and a validation email with a token is sent back to the provided e-mail. </p>
  
  <p>However, if the user submits a wrong e-mail address and tries to submit another one, the email address in the partial_pipeline parameter in the session dictionary is not updated, thus, the validation is always sent to the first e-mail address provided. </p>
  
  <p>I think each time a partial pipeline is started, existing one should be checked and the session parameters, such as the email address, should be updated with the new ones.</p>
  
  <p>Sometime ago I have created a ticket for this issue but there hadn't been an update on that.
  <a href="https://github.com/omab/python-social-auth/issues/325" rel="nofollow">https://github.com/omab/python-social-auth/issues/325</a></p>
  
  <p>Did anyone faced the same problem? Is there a way around it?</p>
  
  <p>Thanks for any help.</p>