Currently ProgressBar is used to monitor upload progress of attachments.
But there's two cases where the associated DOM element may be removed:
- In the champs editor, when the list scrolls, DOM elements are removed
and added dynamically by React;
- In the user form, the user might start an upload on a repetition, and
then remove the associated row during the download.
In both those cases, we don't want the missing DOM element to trigger
an error.
