Hide/show prompt feature does not handle errors thrown from print

[CuriousGeorgiy]

Consider the following snippet:

require('fiber').create(function() while true do pcall(function() print(setmetatable({}, {__tostring = error})) end) require('fiber').sleep(1) end end)

This code constantly erases the prompt and, AFAIC, the memory allocated in console_hide_prompt is also leaked, since after_cb never gets called:

tarantool/src/lua/print.lua

Lines 8 to 14 in a82c246

	if M.before_cb ~= nil then
	M.before_cb()
	end
	M.raw_print(...)
	if M.after_cb ~= nil then
	M.after_cb()
	end

tarantool/src/box/lua/console.c

Lines 340 to 366 in a82c246

	/**
	* Show saved readline's output and free saved strings.
	*/
	static void
	console_show_prompt(void)
	{
	if (!console_can_hide_show_prompt())
	return;
	rl_set_prompt(saved_prompt);
	free(saved_prompt);
	saved_prompt = NULL;
	if (saved_line_buffer == NULL) {
	rl_replace_line("", 0);
	} else {
	rl_replace_line(saved_line_buffer, saved_line_buffer_len);
	}
	free(saved_line_buffer);
	saved_line_buffer = NULL;
	saved_line_buffer_len = 0;
	rl_point = saved_point;
	saved_point = 0;
	rl_redisplay();
	}