segmentation fault in imap fetch function

[yjm6560]

mailio/src/imap.cpp

Lines 341 to 347 in 75db981

	void imap::fetch(unsigned long message_no, message& msg, bool is_uid, bool header_only)
	{
	list<messages_range_t> messages_range;
	messages_range.push_back(imap::messages_range_t(message_no, message_no));
	map<unsigned long, message> found_messages;
	fetch(messages_range, found_messages, is_uid, header_only, msg.line_policy());
	msg = std::move(found_messages.begin()->second);

imap server doesn't send untagged response if uid or message-sequence number requested in FETCH command doesn't exist.
it sends just only tagged response with OK status in that situation.

msg = std::move(found_messages.begin()->second); 

So above code line can generate segmentation fault since it trys to access found_messages.begin() even though there is no element in it.

How about moving the logic which checks if the uid data exists to following handling tagged response?

mailio/src/imap.cpp

Lines 445 to 460 in 75db981

	else if (parsed_line.tag == to_string(tag_))
	{
	if (parsed_line.result.value() == tag_result_response_t::OK)
	{
	has_more = false;
	for (const auto& ms : msg_str)
	{
	message msg;
	msg.line_policy(line_policy, line_policy);
	msg.parse(ms.second);
	found_messages.emplace(ms.first, move(msg));
	}
	}
	else
	throw imap_error("Fetching message failure.");
	}

Of course, it is good to check if found_messages is empty before calling begin()