Issue Summary

Trying to set a field as required when editing the fields of a request type does not work when the request type is in use by the email channel.

Steps to Reproduce

1. Set up an Email channel
2. Go to Project Settings > request types, and edit the fields of the request type in use by the Email Channel: 
3. Try adding a field a setting it as required.

Expected Behavior

A warning message is shown, indicating "The request type is used by the email channel and Jira Service Desk cannot fill field <Field name> automatically from emails. Learn more"

Actual Behavior

Nothing happens when pressing the button Update, and if we check the developer tools, we get:

• An error in the network tab like the following:
  

  {
      "errors": [
          {
              "errorMessage": "This request type is used by the email channel and Jira Service Management cannot fill in field XXXXX automatically from emails."
          }
      ],
      "reasonKey": "sd.email.invalid.request.type.used",
      "reasonCode": "412"
  }
  

• An error in the console tab like the following:

  PUT <Jira_BASE_URL>/rest/servicedesk/1/servicedesk/1/request-type-fields/visible/26 412 (Precondition Failed)