Improve guarding

[bouwew]

The missing guarding might be causing this: https://community.home-assistant.io/t/plugwise-anna-heating-state-incorrect-after-core-update-2022-3/402064

[bouwew]

Indeed, this solves plugwise/plugwise-beta#250

[codecov]

Codecov Report

Merging #164 (bc34f67) into main (08e965b) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #164   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines         2054      2076   +22     
=========================================
+ Hits          2054      2076   +22     

Impacted Files	Coverage Δ
plugwise/__init__.py	100.00% <100.00%> (ø)
plugwise/helper.py	100.00% <100.00%> (ø)
tests/test_smile.py	100.00% <100.00%> (ø)

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