[共通] fix #1192

Author: Reputeless

Siv3D/src/Siv3D/JSON/SivJSON.cpp

@@ -539,14 +539,14 @@ namespace s3d
 
 	JSON& JSON::operator =(const JSON& other)
 	{
-		m_detail = std::make_shared<detail::JSONDetail>(*other.m_detail);
+		m_detail->get() = other.m_detail->get();
 		m_isValid = other.m_isValid;
 		return *this;
 	}
 
 	JSON& JSON::operator =(JSON&& other) noexcept
 	{
-		*m_detail = std::exchange(*other.m_detail, detail::JSONDetail{});
+		m_detail->get() = std::move(other.m_detail->get());
 		m_isValid = std::exchange(other.m_isValid, true);
 		return *this;
 	}