message: fix panic on invalid payload end index
diff: @@ -1023,7 +1023,7 @@ fn generate_packet_trait_impls(cx: &mut GenContext,
  start = "start".to_owned();
  }
  if !payload_bounds.upper.is_empty() {
  - pre = pre + &format!("let end = {};", payload_bounds.upper)[..];
  + pre = pre + &format!("let end = min({}, _self.packet.len());", payload_bounds.upper)[..];
  end = "end".to_owned();
  }
  cx.push_item_from_string(format!("impl<'a> ::pnet::packet::{mutable}Packet for {name}<'a> {{
  @@ -1033,6 +1033,7 @@ fn generate_packet_trait_impls(cx: &mut GenContext,
  #[inline]
  #[cfg_attr(feature = \"clippy\", allow(used_underscore_binding))]
  fn payload{u_mut}<'p>(&'p {mut_} self) -> &'p {mut_} [u8] {{
  + use std::cmp::min;
  let _self = self;
  {pre}
  if _self.packet.len() <= {start} {{
  