fix: errors from less

[alexander-akait]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

fixes #400

Breaking Changes

No

Additional Info

Some plugins can change error message and remove the filename property

[codecov]

Codecov Report

Merging #401 (224b5e9) into master (78befcd) will decrease coverage by 0.81%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master     #401      +/-   ##
==========================================
- Coverage   97.36%   96.55%   -0.82%     
==========================================
  Files           4        4              
  Lines         114      116       +2     
  Branches       25       27       +2     
==========================================
+ Hits          111      112       +1     
- Misses          3        4       +1     

Impacted Files	Coverage Δ
src/index.js	100.00% <ø> (ø)
src/LessError.js	86.66% <50.00%> (-5.65%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 78befcd...224b5e9. Read the comment docs.