ModelService: Cannot add model because it already exists!

[gregoriopellegrino]

When opening a file from within a ZIP/EPUB, closing it, and then trying
to open it again (without reloading the page), the app throws the
following error:

ModelService: Cannot add model because it already exists!

The editor stops working and the file cannot be edited until the page
is manually refreshed.

Steps to reproduce

1. Open zipadee.vercel.app
2. Load a ZIP or EPUB file
3. Click on a file to open it in the editor
4. Close the file (or navigate away)
5. Click on the same file again to reopen it
6. → Error appears: ModelService: Cannot add model because it already exists!