Generates namespace objects when not tree-shaking

[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 #4174

Description

When tree shaking was turned off, sometimes namespace objects were not generated. This is fixed here.

[github-actions]

Thank you for your contribution! ❤️

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

npm install rollup/rollup#gh-4174-no-treeshake-namespace

or load it into the REPL:
https://rollupjs.org/repl/?pr=4175

[codecov]

Codecov Report

Merging #4175 (2c0f8e1) into master (7435d31) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4175   +/-   ##
=======================================
  Coverage   98.33%   98.33%           
=======================================
  Files         202      202           
  Lines        7219     7220    +1     
  Branches     2111     2111           
=======================================
+ Hits         7099     7100    +1     
  Misses         58       58           
  Partials       62       62           

Impacted Files	Coverage Δ
src/Module.ts	100.00% <100.00%> (ø)

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