Don't handle EH/NP Helpers if they don't exist

[malept]

• I have read the contribution documentation for this project.
• I agree to follow the code of conduct that this project follows, as appropriate.
• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable).
• The testsuite passes successfully on my local machine (if applicable).

Summarize your changes:

Don't try to modify helper plists, etc., if they don't exist.

Tested manually with the latest 4.0 nightly. (I'm not using that in the tests because the testsuite downloads way too many Electron versions as it is.)

[codecov]

Codecov Report

Merging #894 into master will increase coverage by 5.51%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           master   #894      +/-   ##
========================================
+ Coverage   94.48%   100%   +5.51%     
========================================
  Files          12     12              
  Lines         617    619       +2     
========================================
+ Hits          583    619      +36     
+ Misses         34      0      -34

Impacted Files	Coverage Δ
mac.js	100% <100%> (+24.26%)	⬆️
ignore.js	100% <0%> (+2.32%)	⬆️

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