message: wasmer_instance_call: allow null params
  allow null params if params_len is zero
diff: @@ -322,7 +322,7 @@ pub unsafe extern "C" fn wasmer_instance_call(
  return wasmer_result_t::WASMER_ERROR;
  }
  - if params.is_null() {
  + if params_len > 0 && params.is_null() {
  update_last_error(CApiError {
  msg: "params ptr is null".to_string(),
  });
  @@ -330,8 +330,17 @@ pub unsafe extern "C" fn wasmer_instance_call(
  return wasmer_result_t::WASMER_ERROR;
  }
  - let params: &[wasmer_value_t] = slice::from_raw_parts(params, params_len as usize);
  - let params: Vec<Val> = params.iter().cloned().map(|x| x.into()).collect();
  + let params: Vec<Val> = {
  + if params_len == 0 {
  + vec![]
  + } else {
  + slice::from_raw_parts::<wasmer_value_t>(params, params_len as usize)
  + .iter()
  + .cloned()
  + .map(|x| x.into())
  + .collect()
  + }
  + };
  let function_name_c = CStr::from_ptr(name);
  let function_name_r = function_name_c.to_str().unwrap();
  