`list-prs-for-file` warns you while you're editing the same PR #3934

1. Open a PR
2. Edit one of its file
3. End up on a page like: https://github.com/fregante/ghat/edit/update-existing/lib.js?pr=%2Ffregante%2Fghat%2Fpull%2F22

Note: It contains a pr parameter that points to the PR 22.

list-prs-for-file shows this message… but you're currently editing that PR, so there's nothing to worry about.

<img width="325" alt="Screen Shot 4" src="https://user-images.githubusercontent.com/1402241/106528064-bf81b280-64ad-11eb-84ae-36f714bae9cb.png">

The current PR should be excluded from the list when possible (if the pr parameter appears in the URL)