Warning when opening readonly files

It would be nice if there was a warning if you’re opening a readonly file. My team uses SVN for art assets and sometimes forget to lock the file (making it read/write) before starting Aseprite. They make changes and the save and get an error. The problem is if they go an unlock the file, it might bring down a more correct version and if they save all the new changes will get stomped.

If there was a warning about the file being readonly, at least they would lock the file before making changes.

Yes, we know about TortoiseSVN and it does solve some issues, but most of my art team are on Macs.