commit message of a single space is unfixable via the Web

[Paul Collins]

Today a bot somehow set the commit message on an MP to a single space. This turns out to have the effect of hiding the commit message and its associated widgetry entirely, making it impossible to edit via the UI.

Here's an example MP that demonstrates the problem. Verified in Firefox 67 and Chromium 73.0.3683.86.

https://code.launchpad.net/~pjdc/launchpad/example-with-invisible-commit-message/+merge/367818

Of course it's trivial to fix via the API, but most people aren't going to know this.

[Paul Collins (pjdc)]

Fixing via API:

$ lp-shell production devel
>>> mp = lp.load('~user/project/branch/+merge/1234567')
>>> mp.commit_message = 'my commit message'
>>> mp.lp_save()
>>> _