Any given plugin erroring or adding warning messages to the output forbids the user to connect Jetpack from wp-admin

[oskosk]

The Connect buttons that Jetpack adds to wp-admin (notices and the Jetpack Admin page) rely on a call to the plugin's REST API for fetching the connection URL. If any given plugin is erroring or adding messages to the output, this will make the connect URLs be wrong and thus the buttons won't work.

Steps to reproduce the issue

1. Have a disconnected site
2. Edit something to echo a string anywhere.
3. Reach the Jetpack admin page.
4. Click the "Connect Jetpack" button
5. expect a 404 or something similar

What I expected

I expected that not to happen but it's fine. It can be circumvented somehow.

What happened instead

Wasn't able to connect my Jetpack