Possible bug: header name doesn't get regex-matched in non-strict mode if the corresponding value is empty

[tsilia]

Hello.
In the mime.cpp there could be a logic error introduced along with adding support for non-strict mode. As you can see in the source file:

mailio/src/mime.cpp

Lines 703 to 711 in 3fccce6

	if (header_value.empty())
	if (_strict_mode)
	throw mime_error("Parsing failure, header name or value empty: " + header_line);
	else
	return;
	smatch m;
	if (!regex_match(header_name, m, HEADER_NAME_REGEX))
	throw mime_error("Format failure of the header name `" + header_name + "`.");

in case when the method accepts an empty header_value, header_name wouldn't get checked with regex_match because the code would have returned before this check. But it seems reasonable to check the header_name regardless of whether the mode is strict or not.

I've checked this using the following code and the behaviour was different in two cases: empty value and non-empty value. In the second case an exception is thrown:

msg_wrapper msg;
msg.strict_mode(false);
msg.strict_codec_mode(false);
std::string header_name, header_value;
msg.ParseHeader("Invalid header: ", header_name, header_value);
msg.ParseHeader("Invalid header: non-empty value", header_name, header_value); // exception

(msg_wrapper is a thin wrapper class as mime::parse_header_name_value() method is protected).