Return correct values for unkown namespace members

[lukastaegert]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

• resolves [v3] treeshake unexpectedly assumed "a" in b==b.a != null #4680

Description

For some reason, I assumed the logic to retrieve explicit values from namespaces would only be relevant for Symbol.toStringTag. No idea why I thought that, here is the fix.

[github-actions]

Thank you for your contribution! ❤️

You can try out this pull request locally by installing Rollup via

npm install rollup/rollup#gh-4680-unknown-namespace-value

or load it into the REPL:
https://rollupjs.org/repl/?pr=4684

[codecov]

Codecov Report

Merging #4684 (acd6240) into master (1619ef2) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4684   +/-   ##
=======================================
  Coverage   99.02%   99.02%           
=======================================
  Files         215      215           
  Lines        7570     7572    +2     
  Branches     2096     2097    +1     
=======================================
+ Hits         7496     7498    +2     
  Misses         24       24           
  Partials       50       50           

Impacted Files	Coverage Δ
src/ast/variables/NamespaceVariable.ts	100.00% <100.00%> (ø)

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[rollup-bot]

This PR has been released as part of rollup@3.2.3. You can test it via npm install rollup.