[DAR-4308][External] Allow fetch_remote_files to return files that have not yet finished processing

[JBWilkie]

Problem

In DAR-2981, we allowed fetch_remote_files to return the layout of a remote file

However, this change assumed there would always be a layout, and for non-processed files, the layout is not yet populated, leading to a syntax error

Solution

Allow fetch_remote_files to return non-processed files by making return of layout optional

Changelog

Allow fetch_remote_files to return non-processed files

[linear]

DAR-4308 Allow `fetch_remote_files` to return files that have not yet finished processing