fix: handle only valid srcset tags

[alexander-akait]

This PR contains a:

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

Motivation / Use-Case

handle only valid srcset tags

Breaking Changes

No

Additional Info

No

[codecov]

Codecov Report

Merging #253 into master will not change coverage by %.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #253   +/-   ##
=======================================
  Coverage   95.61%   95.61%           
=======================================
  Files           8        8           
  Lines         319      319           
  Branches       84       84           
=======================================
  Hits          305      305           
  Misses         13       13           
  Partials        1        1           

Impacted Files	Coverage Δ
src/plugins/source-plugin.js	99.50% <ø> (ø)

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