Possible data loss on update with different content type.

[damooo]

When one try to update representation of a resource to a new one with different content-type, the operation is prone to data-loss when using fs-accessor.

It first removes file corresponding to previous rep wityh out backup here:

CommunitySolidServer/src/storage/accessors/FileDataAccessor.ts

Line 89 in 7eb9380

await this.verifyExistingExtension(link);

Then performs many fallible operations of writing metadata, and new data, etc. Failing of any one effectively deletes old rep, with out updating.

[joachimvh]

Not sure why we did it in that order. Could perhaps be something to do with potential conflicts in the underlying resource mapper. But if possible it would indeed be better to reverse the order. Still potentially has issues but lower chances of data loss if something goes horribly wrong.