Update json.cpp

[St0fF-NPL-ToM]

Description

JSONparser collects messages, but at the end they were dumped to nirvana. Let's output those as warnings!

Type of change

• New feature (non-breaking change which adds functionality)
  • Make-Available of already existing, but maybe forgotten feature

How Has This Been Tested?

• Reading erroneous JSON files

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules