fix compilation error when RYML_NO_DEFAULT_CALLBACKS is defined

[toge]

On 0.11.0, there are compilation errors:

src/c4/yml/common.cpp:136:19: error: ‘error_’ was not declared in this scope; did you mean ‘error_t’?
  136 |     m_error_basic(error_),
      |                   ^~~~~~
      |                   error_t
src/c4/yml/common.cpp:140:1: error: expected identifier before ‘{’ token
  140 | {
      | ^

This PR trys to fix these.

[biojppm]

Thanks for catching this. I see now that this case is not covered in the CI. I will follow up by adding those tests.

[toge]

@biojppm
Thank you for quick action!