Issue Summary

When editing a webhook you cannot save without re-inputting mandatory fields

Steps to Reproduce

1. Create a webhook for a repository at Repository Settings > Webhooks > Create Webhook
2. Edit the webhook
3. Add a new event
4. Save

Expected Results

The webhook updates.

Actual Results

The form requires you to re-enter the webhook name and URL (mandatory fields) before allowing you to save despite the field being populated.

Please enter a name
Please enter a URL

Workaround

Re-input the name and URL again before saving.