Even if the LO core code, as called by the Online code, already has
saved the document back to the file from which it was loaded, in order
for a file provider extension like NextCloud to notice that, it is
essential to call saveToURL:forSaveOperation:completionHandler:. The
contentsForType:error: method can just return a NSFileWrapper for the
same, already saved, file, though.
Change-Id: Ic063c8603ca38930083866d973e500336cad517e
