File write error: undefined

The command `Page.cmd "fileWrite"` is showing a UI message error with the text: `File write error: undefined` but there is nothing in the debug logs nor console.

**To Reproduce:**

1 - Download the site Antilibrary.bit and add the spanish DB (just because it is the smallest one)
2 - Import this CSV ([goodreads_library_export.txt](https://github.com/HelloZeroNet/ZeroNet/files/627852/goodreads_library_export.txt)) on the Goodreads CSV Importer in Antilibrary.bit (inside My Books)

The file will import and you should get this error after 2 or 3 seconds.
I can't find a way to debug this problem because it seems that this error is showing just in the UI.

Start by reproducing the Goodreads CSV Importer failure in Antilibrary.bit with the linked export, then trace the Page.cmd "fileWrite" entry point and the UI path that displays the error. Check how the underlying file-write failure is propagated and logged; done means the import no longer reports an undefined error and useful diagnostic output is available.

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