Don't crash when a message is split in the middle of the payload length field.

Author: thejoelw

lib/mint/web_socket/frame.ex

@@ -259,15 +259,15 @@ defmodule Mint.WebSocket.Frame do
        ),
        do: {:ok, payload_length, rest}
 
-  defp decode_payload_length(<<127::integer-size(7)>>), do: :buffer
+  defp decode_payload_length(<<127::integer-size(7), _rest::bitstring>>), do: :buffer
 
   defp decode_payload_length(
          <<126::integer-size(7), payload_length::unsigned-integer-size(8)-unit(2),
            rest::bitstring>>
        ),
        do: {:ok, payload_length, rest}
 
-  defp decode_payload_length(<<126::integer-size(7)>>), do: :buffer
+  defp decode_payload_length(<<126::integer-size(7), _rest::bitstring>>), do: :buffer
 
   defp decode_payload_length(<<payload_length::integer-size(7), rest::bitstring>>)
        when payload_length in 0..125,