Fix Edit/Delete dialog overflow caused by long username in nuxeo-document-comment-thread

If a user with a long (100+ character) identifier makes a nuxeo-comment in a nuxeo-document-comment-thread used in a bounded pane (such as in nuxeo-document-page), the Edit/Delete dialog can overflow out of the browser window; either being difficult to access or displaying small scrollbars around the dialog.

Steps to Reproduce:

1. In Web UI, create a user with a long (100+ character) username, for example:

longlonglonglonglonglonglonglonglonglonglonglonglonglonglonglonglonglonglonglonglonglonglonglonglonglonguser

2. Navigate to any commentable Document and create a comment of shorter length than the username.

Expected result: the Edit/Delete dialog opens toward the left such that it's not cut off by the right-side vertical boundary.

Actual result: the Edit/Delete dialog opens toward the right as it usually does, causing it to overflow (see screenshot).