dd-trace-cpp malformed unicode header values may cause crash

dd-trace-cpp is the Datadog distributed tracing for C++. When the library fails to extract trace context due to malformed unicode, it logs the list of audited headers and their values using the `nlohmann` JSON library. However, due to the way the JSON library is invoked, it throws an uncaught exception, which results in a crash. This vulnerability has been patched in version 0.2.2.