make commit-statuses popup can be shown correctly. (#17447)

Close #17443

Maybe we do not need to backport this PR, the bug doesn't break daily usage.

After the fix, the commit statuses popup can show a lot of lines with scroll bars:

![image](https://user-images.githubusercontent.com/2114189/139026160-f01b484c-6207-494a-a190-a6dd184ceb2b.png)

web_src/js/features/repo-legacy.js

@@ -267,10 +267,13 @@ export async function initRepository() {
 
   // Commit statuses
   $('.commit-statuses-trigger').each(function () {
+    const positionRight = $('.repository.file.list').length > 0 || $('.repository.diff').length > 0;
+    const popupPosition = positionRight ? 'right center' : 'left center';
     $(this)
       .popup({
         on: 'click',
-        position: ($('.repository.file.list').length > 0 ? 'right center' : 'left center'),
+        lastResort: popupPosition, // prevent error message "Popup does not fit within the boundaries of the viewport"
+        position: popupPosition,
       });
   });