Improve protections again and player database (#606)

src/json_util.hpp

@@ -0,0 +1,17 @@
+#pragma once
+
+namespace big
+{
+	template <typename ValueType>
+	static inline void set_from_key_or_default(const nlohmann::json& j, const char* key, ValueType& value, ValueType default_value = {})
+	{
+		if (j.contains(key))
+		{
+			j.at(key).get_to(value);
+		}
+		else
+		{
+			value = default_value;
+		}
+	}
+}