updating length() function for of zero length case

[MartinLBeacham]

for circularQueue

 know more

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new JavaScript files are placed inside an existing directory.
• All filenames should use the UpperCamelCase (PascalCase) style. There should be no spaces in filenames.
  Example:UserProfile.js is allowed but userprofile.js,Userprofile.js,user-Profile.js,userProfile.js are not
• All new algorithms have a URL in their comments that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 84.07%. Comparing base (702840b) to head (b883757).

Files	Patch %	Lines
Data-Structures/Queue/CircularQueue.js	0.00%	1 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@ ## master #1654 +/- ## ======================================= Coverage 84.07% 84.07% ======================================= Files 375 375 Lines 19688 19688 Branches 2914 2914 ======================================= Hits 16552 16552 Misses 3136 3136 

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.