Handle empty registration cases

[JR-1991]

The direct upload registration should only proceed if there are files to register.

python-dvuploader/dvuploader/directupload.py

Lines 557 to 566 in bb39bd4

	await _multipart_json_data_request(
	session=session,
	json_data=novel_json_data,
	url=novel_url,
	)
	await _multipart_json_data_request(
	session=session,
	json_data=replace_json_data,
	url=replace_url,