Note: 

This needs to be ported to release/1.3

Steps to reproduce

• Create pipeline for repo where you have no push access
• After pipeline is build, click on Edit pipeline, it renders an empty editor page, see attachment.

What should happen is a warning that push access will be required to edit it. 

In the background editor calls API to fetch Jenkinsfile but API responds with 428 as provided access token or the user doesn't have push access.

Unable to find source-code formatter for language: json. Available languages are: actionscript, html, java, javascript, none, sql, xhtml, xml428 (Precondition Required)

{
  "message" : "You do not have permission to push changes to cloudbees/test-mvn-app",
  "code" : 428,
  "errors" : [ ]
}