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 (502775b) to head (1f736db).
Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #10   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            1         1           
  Lines           42        42           
  Branches        10        10           
=========================================
  Hits            42        42           

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