fix(filters): add more variable undefined checks in multiple-select external lib

[ghiscoding]

• in some rare occasion we had "cannot read 'prop' of undefined" happening. This PR adds more checks to make sure we aren't trying to read a method of an undefined element

[codecov]

Codecov Report

Merging #710 (11876c4) into master (e50a060) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #710   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files          159       159           
  Lines        10626     10626           
  Branches      3756      3756           
=========================================
  Hits         10626     10626           

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