Fix exception when going to debates new URL directly as non-logged user

[andreslucena]

🎩 What? Why?

There's an exception when visiting a new debates form page directly as a visitor. This PR fixes it.

I've also added some specs for this same problem in components with the "Participants can create ..." setting: Proposals and Meetings.

📌 Related Issues

• Fixes https://meta.decidim.org/processes/bug-report/f/210/proposals/17699

Testing

1. Sign in as admin
2. Enable debates created by participant in a debates component in a participatory space
3. Go to the debates index page
4. Click in the "New debate" button
5. Copy the URL
6. Open it in a new incognito/private session in your browser
7. (Without the patch) see an exception
8. (With the patch) see that you're redirected to the login page

♥️ Thank you!

[alecslupu]

The fix works as expected, but i would change a spec to respect the consistency with the rest of the specs added within this PR.

[andreslucena]

The fix works as expected, but i would change a spec to respect the consistency with the rest of the specs added within this PR.

As we've talked currently the three specs are controller specs so they're consistent in that aspect. Maybe can you give it another look 😄 ?