Cleanup after Keyboard interrupt correctly

[Cadair]

Fixes #60

[codecov]

Codecov Report

Merging #104 (b3d52d5) into main (ceaa210) will decrease coverage by 2.35%.
The diff coverage is 70.66%.

@@            Coverage Diff             @@
##             main     #104      +/-   ##
==========================================
- Coverage   93.13%   90.77%   -2.36%     
==========================================
  Files           5        5              
  Lines         568      607      +39     
==========================================
+ Hits          529      551      +22     
- Misses         39       56      +17     

Impacted Files	Coverage Δ
parfive/main.py	91.17% <0.00%> (-2.77%)	⬇️
parfive/utils.py	90.51% <25.00%> (-4.03%)	⬇️
parfive/downloader.py	90.35% <78.46%> (-2.84%)	⬇️

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