preview:generate-all crashses without an error

While running "preview:generate-all", the app crashes without an error.

I usually read the output of "-vv" and check manually if the last file processed is working or not.
If the file is corrupted, I delete it through the browser (update database), and run the command again, only to crash on a different file

I tried to run the command using --workers=100, but eventually they all crash, quite on the same time
Perhaps they all try to process the same file?
(EDIT: Running 25 tasks, output log shows each worker died on a different file)

My suggestion is to change the forking mechanism to a "per media file" worker

1. The main worker lists all media files;
2. Main thread creates a child process;
3. Handle the media file to child (path argument);
4. Child generate preview;
5. Child die;
6. Return to 2 until list is empty;

--workers defaults to 1; user can input a greater value.
This logic will allow to process all files, without crashing the full queue and needing restart the process.

Start by reproducing preview:generate-all with -vv and different --workers values, then trace the command's worker and media-file processing flow. Done means a failure in one media file does not crash the full queue, remaining files continue processing, and the behavior is covered by an appropriate test or reproducible check.