new_client interface
- Definition：
int _stdcall new_client(int camera, void** client);
- Parameter：
camera：[in]，The handle of camera while is from new_camera.
client：[out]，client object, to be used by other funtion of accessing camera.
- Return：
Return ERROR_OK if success，else refer to the definition of error number
- Explain：
Register a new camera client, it must be called to get a client object before calling some interface of accessing the camera.