OSV-2024-1071 Use-of-uninitialized-value in Poco::Dynamic::Var::~Var

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=42538385 Crash type: Use-of-uninitialized-value Crash state: Poco::Dynamic::Var::Var void Poco::JSON::Object::doStringifystd::1::mapstd::1::basicstringchar, Poco::JWT::Serializer::serialize...