Only check version URL after determining if it was already installed

[WardBrian]

Submission Checklist

• Run unit tests
• Declare copyright holder and open-source license: see below

Summary

Closes #672. This now only checks if the requested version is available after determining that the requested version is not already installed (e.g., right before we would try to download it).

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company):
Simons Foundation

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)

[codecov-commenter]

Codecov Report

Merging #673 (bafb7b1) into develop (7ad7dcc) will increase coverage by 0.47%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #673      +/-   ##
===========================================
+ Coverage    80.44%   80.92%   +0.47%     
===========================================
  Files           69       69              
  Lines        10653    10653              
===========================================
+ Hits          8570     8621      +51     
+ Misses        2083     2032      -51     

see 6 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[ahartikainen]

LGTM