set-default-repositories-type-to-sources: undefined is not an object (evaluating 'link.search') #3908

1. Open a PR like Update to next dom-chef #3904
2. Visit the PR Commits tab
3. Open the profile dropdown
   

This happens because:

1. init is called on every ajax load
2. init attaches a mutation handler
3. when the user opens the dropdown, the handler fires twice, but the second time the selector no longer finds anything