Webhooks not triggered when git_ref_pattern is empty space

[Ines Almeida]

Context:
Launchpad added a feature where when a `git_ref_pattern` is added to a webhook, then that webhook only triggers when the pattern matches the git refs/branches associated with what event triggered the webhook.

Bug description:
When a user sets the `git_ref_pattern` to an empty white space, the webhook will not trigger because the pattern doesn't match. This is quite confusing for a user, because they won't even see a message warning them.

To reproduce:
 - Create a new webhook for a git repository that has a `git_ref_pattern=" "` with scope "Git push"
 - Push a change to a branch in that repository
 - The webhook is not triggered

Possible solutions:
 1) Add validation to the input - we shouldn't allow a white-space as a git-ref-pattern
 2) Or, allow white-spaces, but sanitize the pattern on input by removing white spaces around on submit

[Jürgen Gmach (jugmac00)]

I am all for 1) - do not allow invalid data to enter our systems.