[chirp_devel] Revise handling of empty chunks in yaesu_clone.py

Changes to yaesu_clone. These changes have been tested on a few Yaesu radios, but just to make everyone aware.

[FT-70] #5329 and issue #5647 Revise handling of empty chunks in yaesu_clone.py #5647 Empty chunks no longer counted towards blocks read. #5329 Can now set correct memory size read request, as not getting empty blocks.

If you have a Yaesu radio that uses Yaesu_clone a quick test would be great.

Nicolas