Update asserts hit in DEBUG builds for WinForms WebView

[rjmurillo]

PR Type

What kind of change does this PR introduce?

• Bugfix

What is the current behavior?

When using the debug builds of the WinForms WebView control, some circumstances may trigger an assert that causes delays while using the Visual Studio designer.

What is the new behavior?

Update conditions for which asserts are hit in DEBUG builds only

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Docs have been added/updated which fit documentation template. (for bug fixes / features)
• Sample in sample app has been added / updated (for bug fixes / features)
  • Icon has been created (if new sample) following the Thumbnail Style Guide and templates
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Header has been added to all new source files (run build/UpdateHeaders.bat)
• Contains NO breaking changes

Other information

As a workaround, the compiler constant DEV_DEBUG can be removed to turn off the more aggressive asserts. CC @GraniteStateHacker