The second find_package will cause error

https://github.com/Tencent/rapidjson/blob/24b5e7a8b27f42fa16b96fc70aade9106cf7102f/RapidJSONConfig.cmake.in#L10-L12

cmake 用<PackageName>_DIR 存储configuration file的目录。 RapidJSON_DIR被覆盖后会报错。