Improve HTTP1 invalid header value crash

Before this patch:

    iex> {:ok, conn} = Mint.HTTP1.connect(:http, "httpbin.org", 80) ; Mint.HTTP.request(conn, "GET", "/json", [{"accept", nil}], nil)
    ** (ErlangError) Erlang error: {:bad_generator, nil}
        (mint 1.7.1) lib/mint/http1/request.ex:61: Mint.HTTP1.Request."-validate_header_value!/2-lc$^0/1-0-"/3
        (mint 1.7.1) lib/mint/http1/request.ex:61: Mint.HTTP1.Request.validate_header_value!/2
        (mint 1.7.1) lib/mint/http1/request.ex:26: anonymous fn/2 in Mint.HTTP1.Request.encode_headers/1
        (elixir 1.18.4) lib/enum.ex:2546: Enum."-reduce/3-lists^foldl/2-0-"/3
        (mint 1.7.1) lib/mint/http1/request.ex:9: Mint.HTTP1.Request.encode/4
        (mint 1.7.1) lib/mint/http1.ex:286: Mint.HTTP1.request/5
        iex:4: (file)

After:

    iex> {:ok, conn} = Mint.HTTP1.connect(:http, "httpbin.org", 80) ; Mint.HTTP.request(conn, "GET", "/json", [{"accept", nil}], nil)
    ** (FunctionClauseError) no function clause matching in Mint.HTTP1.Request.validate_header_value!/2

        The following arguments were given to Mint.HTTP1.Request.validate_header_value!/2:

            # 1
            "accept"

            # 2
            nil

        Attempted function clauses (showing 1 out of 1):

            defp validate_header_value!(name, value) when is_binary(value)

        (mint 1.7.1) lib/mint/http1/request.ex:59: Mint.HTTP1.Request.validate_header_value!/2
        (mint 1.7.1) lib/mint/http1/request.ex:26: anonymous fn/2 in Mint.HTTP1.Request.encode_headers/1
        (elixir 1.18.4) lib/enum.ex:2546: Enum."-reduce/3-lists^foldl/2-0-"/3
        (mint 1.7.1) lib/mint/http1/request.ex:9: Mint.HTTP1.Request.encode/4
        (mint 1.7.1) lib/mint/http1.ex:286: Mint.HTTP1.request/5
        iex:4: (file)

The error message is still pretty bad for HTTP2 at the moment though:

    iex> {:ok, conn} = Mint.HTTP2.connect(:https, "httpbin.org", 443) ; Mint.HTTP.request(conn, "GET", "/json", [{"accept", nil}], nil)
    ** (FunctionClauseError) no function clause matching in HPAX.encode_headers/3

        The following arguments were given to HPAX.encode_headers/3:

            # 1
            [{:store_name, "accept", nil}]

            # 2
            %HPAX.Table{
              max_table_size: 4096,
              huffman_encoding: :never,
              entries: [],
              size: 0,
              length: 0
            }

            # 3
            [
              [
                [[[[], <<130>>], [<<4>>, [<<5>>, "/json"]]], <<135>>],
                [<<1>>, ["\v", "httpbin.org"]]
              ],
              [<<15, 43>>, ["\n", "mint/1.7.1"]]
            ]

        Attempted function clauses (showing 2 out of 2):

            defp encode_headers([], table, acc)
            defp encode_headers([{action, name, value} | rest], table, acc) when (action === :store or action === :store_name or action === :no_store or action === :never_store) and is_binary(name) and is_binary(value)

        (hpax 1.0.0) lib/hpax.ex:281: HPAX.encode_headers/3
        (elixir 1.18.4) lib/map.ex:999: Map.get_and_update!/3
        (mint 1.7.1) lib/mint/http2.ex:1134: Mint.HTTP2.encode_headers/4
        (mint 1.7.1) lib/mint/http2.ex:520: Mint.HTTP2.request/5
        iex:4: (file)

Author: wojtekmach

lib/mint/http1/request.ex

@@ -45,7 +45,7 @@ defmodule Mint.HTTP1.Request do
     [Integer.to_string(length, 16), "\r\n", chunk, "\r\n"]
   end
 
-  defp validate_header_name!(name) do
+  defp validate_header_name!(name) when is_binary(name) do
     _ =
       for <<char <- name>> do
         unless is_tchar(char) do
@@ -56,7 +56,7 @@ defmodule Mint.HTTP1.Request do
     :ok
   end
 
-  defp validate_header_value!(name, value) do
+  defp validate_header_value!(name, value) when is_binary(value) do
     _ =
       for <<char <- value>> do
         unless is_vchar(char) or char in ~c"\s\t" do