fix: exception on concurrent download of ParseFile from multiple threads

[techyourchance]

New Pull Request Checklist

• [ x ] I am not disclosing a vulnerability.
• [ x ] I am creating this PR in reference to an issue.

Issue Description

Related issue: #1155

Approach

This PR simplifies the logic of fetchAsync method and then adds a concurrent code that blocks the second (and further) calling threads until the first thread finishes the download of ParseFile (or fails to do so).

TODOs before merging

• [ x ] Add tests
• [ x ] Add changes to documentation (guides, repository pages, in-code descriptions)
• A changelog entry is created automatically using the pull request title (do not manually add a changelog entry)

[parse-github-assistant]

Thanks for opening this pull request!

• 🎉 We are excited about your hands-on contribution!

[mtrezza]

Just removing some empty lines...

[codecov]

Codecov Report

Merging #1179 (d5c50f4) into master (351858c) will not change coverage.
The diff coverage is 0.00%.

@@          Coverage Diff           @@
##           master   #1179   +/-   ##
======================================
  Coverage    0.00%   0.00%           
======================================
  Files         122     122           
  Lines        9962    9970    +8     
  Branches     1343    1345    +2     
======================================
- Misses       9962    9970    +8     

Impacted Files	Coverage Δ
...e/src/main/java/com/parse/ParseFileController.java	0.00% <0.00%> (ø)

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[mtrezza]

Thanks for the fix! Could you take a look at the failing lint test?

[rommansabbir]

Thanks for the fix! Could you take a look at the failing lint test?

I will take a look at the fail and it seems like Spotless not applied.

[rommansabbir]

@techyourchance @mtrezza Closing this PR as created a new PR (#1180) by fixing the CI failing issue for Spotless violations.