Return True if there is no modbus data to write

[Guzz-T]

If we use luxtronik.write(), shi.write() is also called, even though only parameters should be written. This previously led to an invalid result.

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
luxtronik
__main__.py	25	25	0%	3–66
datatypes.py	450	1	99%	147
discover.py	58	1	98%	63
luxtronik/cfi
interface.py	175	3	98%	167–168, 256
luxtronik/definitions
__init__.py	208	1	99%	216
luxtronik/scripts
__init__.py	35	5	86%	7–16, 51
discover_shi.py	60	60	0%	8–98
dump_cfi.py	14	6	57%	18–25, 29
dump_shi.py	15	6	60%	21–28, 32
performance_shi.py	63	63	0%	7–89
update_screen.py	105	82	22%	6, 20–41, 46–48, 51–61, 64, 70–75, 78, 81–85, 88–92, 95–97, 100–103, 106–111, 115–116, 119–126, 129–136
watch_cfi.py	32	16	50%	36–47, 50–56, 60
watch_shi.py	33	16	52%	38–49, 52–58, 62
luxtronik/shi
interface.py	337	3	99%	438, 519, 527
TOTAL	2432	288	88%

Tests	Skipped	Failures	Errors	Time
378	0 💤	0 ❌	0 🔥	17.932s ⏱️