A few small fixes

[SergeyMenshykh]

Motivation and Context

This PR has two fixes to allow this app to work with OpenAPI skills.

Description

The first fix prevents endless while loop, and the other one read http operation body as as string.

Contribution Checklist

• [x] The code builds clean without any errors or warnings
• [x] The PR follows SK Contribution Guidelines (https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
• [x] The code follows the .NET coding conventions (https://learn.microsoft.com/dotnet/csharp/fundamentals/coding-style/coding-conventions) verified with dotnet format
• [x] All unit tests pass, and I have added new tests where possible
• [ ] I didn't break anyone :smile: