fix compile warning

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
fix invalid memory access bug introduced by filter support patch

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
add function filter sample script into README.md

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>