fix: issue #661 - don't try to access a zero length body

[orinem]

PR Checklist

• Unit Tests have been added for new changes
• All commented code has been removed

What are you changing?

Fix for issue #661.

Anything the reviewer should know when reviewing this PR?

See discussion for issue #661. The test uses the exact message that caused the problem. Note that in spite of 'body' not being optional in HttpZResponseModel, it wasn't present in this case.

Also fixed text for the previous last test, the return is an empty string, not null.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@fc56834). Click here to learn what that means.
The diff coverage is 100.00%.

❗ Current head 3033315 differs from pull request most recent head 53b37c5. Consider uploading reports for the commit 53b37c5 to get more accurate results

@@           Coverage Diff           @@
##             main     #734   +/-   ##
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  Coverage        ?   93.36%           
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  Files           ?       78           
  Lines           ?     3288           
  Branches        ?      528           
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  Hits            ?     3070           
  Misses          ?      218           
  Partials        ?        0           

Impacted Files	Coverage Δ
src/utils/parseWSManResponseBody.ts	92.85% <100.00%> (ø)

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