fix: crash when converting invalid JSON object on Swift SDK

[zhu-xiaowei]

Description

1. fix crash when converting invalid JSON object on Swift SDK

General Checklist

• Added new tests to cover change, if needed
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• If breaking change, documentation/changelog update with migration instructions

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (e9e2110) to head (83494c5).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #12   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            4         4           
  Lines           99        99           
=========================================
  Hits            99        99           

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