filter::graph::Graph::input()/output() bugs,cause memory leak and does not support more than 2 inputs/outputs

[damaitou]

I paste the output() code here and add comment to the line which bug occurs. same question to the input() code.

pub fn output(mut self, name: &str, pad: usize) -> Result<Self, Error> {
unsafe {
let mut context = self.graph.get(name).ok_or(Error::InvalidData)?;
let output = avfilter_inout_alloc();

        if output.is_null() {
            panic!("out of memory");
        }

        let name = CString::new(name).unwrap();

        (*output).name = av_strdup(name.as_ptr());
        (*output).filter_ctx = context.as_mut_ptr();
        (*output).pad_idx = pad as c_int;
        (*output).next = ptr::null_mut();

        if self.outputs.is_null() {
            self.outputs = output;
        } else {
            (*self.outputs).next = output;  //BUG here. output should be append to the tail of the linklist, should not append to the head. this cause memory leaks and does not support more than 2 outputs.
        }
    }

    Ok(self)
}