Return 0% when download totalBytes is 0 or undefined

[diracdeltas]

Fix #10264

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.

Test Plan:
Download a large file and hit 'pause' immediately. It should not show Infinity% downloaded.

Reviewer Checklist:

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[codecov-io]

Codecov Report

Merging #10652 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #10652      +/-   ##
==========================================
+ Coverage   54.16%   54.17%   +0.01%     
==========================================
  Files         247      247              
  Lines       21554    21558       +4     
  Branches     3338     3342       +4     
==========================================
+ Hits        11674    11679       +5     
+ Misses       9880     9879       -1

Flag	Coverage Δ
#unittest	54.17% <100%> (+0.01%)	⬆️

Impacted Files	Coverage Δ
js/state/downloadUtil.js	100% <100%> (+1.56%)	⬆️

[bbondy]

++

[bbondy]

Actually I think we didn't used to show anything at all. Will this show 0% always for downloads that don't specify a content length in the reply?

[diracdeltas]

@bbondy i think it would have shown NaN% or Infinity% previously

[bbondy]

I mean originally we didn't show anything at all. There is a case where there is no known % because we don't know the content length being downloaded. For example if that happens with a 3GB file we shouldn't show 0% the whole time it is downloading. Do you know if that will happen?

[diracdeltas]

@bbondy pretty sure that is unaffected by this PR. looks like that check happens in app/renderer/components/download/downloadItem.js using totalBytes

[bsclifton]

Looks and works great! 😄

I updated the method to check for falsey input and then added some more tests in general (thanks for creating tests for this module!) 😄