Comment 0 for bug 1771767

# Summary

When registering a snap name that already exists filing a dispute is not working.

# Steps to reproduce

## On dashboard

- https://dashboard.snapcraft.io/register-snap/
- Register a snap that already exists (toto, firefox...)
- Message shows to file a dispute
- File a dispute
- Page reloads with same error message

## On API

- Register a snap that already exists
/dev/api/register-name/
{
  "snap_name": "toto"
}

Response:
409 Conflict
{
 "error_list": [{'message': "'toto' is already registered.", 'code': 'already_registered'}]
}

- File a dispute
/dev/api/register-name/
{
  "snap_name": "toto",
  "registrant_comment": "I want this awesome snap name"
}

Response:
409 Conflict
{
 "error_list": [{'message': "'toto' is already registered.", 'code': 'already_registered'}]
}

# Expected behaviour

## On dashboard

- https://dashboard.snapcraft.io/register-snap/
- Register a snap that already exists (toto, firefox...)
- Message shows to file a dispute
- File a dispute
- Redirect to a 'thank you page' or else

## On API

- Register a snap that already exists
/dev/api/register-name/
{
  "snap_name": "toto"
}

Response:
409 Conflict
{
 "error_list": [{'message': "'toto' is already registered.", 'code': 'already_registered'}]
}

- File a dispute
/dev/api/register-name/
{
  "snap_name": "toto",
  "registrant_comment": "I want this awesome snap name"
}

Response:
409 Conflict
{
 "error_list": [{'message': "You already registered a claim for 'toto'.", 'code': 'already_registered'}]
}