Fix uploading files in rare cases

[SystemKeeper]

Sometimes trying to read files with NSFileCoordinatorReadingForUploading fails with

Error Domain=NSOSStatusErrorDomain Code=-10810 "(null)" UserInfo={_LSLine=213, _LSFunction=normalizeError}

At the same time NSFileCoordinatorReadingWithoutChanges seems to work in these cases. So now we use NSFileCoordinatorReadingWithoutChanges as a fallback, in case NSFileCoordinatorReadingForUploading failed.

Best reviewed as https://github.com/nextcloud/talk-ios/pull/1457/files?diff=unified&w=1