Handle default exporting global variables

[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:
May or may not solve #3523

Description

When reworking the default export short-cut logic, I did not consider in some cases what should happen if a global variable is default-exported. This fixes it.

[rollup-bot]

Thank you for your contribution! ❤️

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

npm install rollup/rollup#gh-3523-export-default-global

or load it into the REPL:
https://rollupjs.org/repl/?circleci=10770

[codecov]

Codecov Report

Merging #3526 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3526   +/-   ##
=======================================
  Coverage   96.22%   96.22%           
=======================================
  Files         176      176           
  Lines        5982     5984    +2     
  Branches     1763     1765    +2     
=======================================
+ Hits         5756     5758    +2     
  Misses        112      112           
  Partials      114      114           

Impacted Files	Coverage Δ
src/Chunk.ts	99.77% <100.00%> (ø)
src/Module.ts	98.91% <100.00%> (+<0.01%)	⬆️

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