prevents Perl warning WS2000

[elektron-bbs]

• Please check if the PR fulfills these requirements

• Tests for the changes have been added / modified (needed for for bug fixes / features)
• commandref has been added / updated (needed for bug fixes / features)

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

• Bugfix (please link issue)
• Feature enhancement
• Documentation update
• Unittest enhancement
• other

• What is the current behavior?
  (You can also link to an open issue here, if this describes the current behavior)
  PERL WARNING: Use of uninitialized value in join or string at FHEM/lib/SD_Protocols.pm line 1436.

• What is the new behavior (if this is a feature change)?
  no PERL WARNING

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  no

• Other information:

[codecov]

Codecov Report

Merging #1083 (c65c746) into master (2d2517a) will increase coverage by 0.13%.
The diff coverage is 25.00%.

@@            Coverage Diff             @@
##           master    #1083      +/-   ##
==========================================
+ Coverage   63.50%   63.63%   +0.13%     
==========================================
  Files         128      130       +2     
  Lines        9475     9529      +54     
  Branches     1503     1510       +7     
==========================================
+ Hits         6017     6064      +47     
  Misses       2300     2300              
- Partials     1158     1165       +7     

Flag	Coverage Δ
fhem	55.39% <25.00%> (+0.14%)	⬆️
modules	63.63% <25.00%> (+0.13%)	⬆️
perl	90.59% <25.00%> (+0.10%)	⬆️
unittests	63.63% <25.00%> (+0.13%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
FHEM/lib/SD_ProtocolData.pm	100.00% <ø> (ø)
FHEM/lib/SD_Protocols.pm	79.45% <25.00%> (+0.31%)	⬆️
t/FHEM/14_BresserTemeo/09_parseDatat.t	80.00% <0.00%> (ø)
t/FHEM/14_SD_WS07/09_parseDatat.t	80.00% <0.00%> (ø)
FHEM/10_SD_Rojaflex.pm	71.54% <0.00%> (+0.40%)	⬆️

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