windows console input sometimes drop leading charactors.

[YO4]

In win32.c, is_readable_console() drops some kind of valid input character.
As a result, the first character(s) of STDIN.gets can be lost.

1. codepoint(in unicode) lower bytes has 0x00. \u0100,\u0400,\u2200, CJK charactors, etc.
2. ALT+NUMPAD sequence, via classic console(conhost.exe). They generates VK_ALT, key_up, UnicodeChar != 0.

This fixes both situations.

[nobu]

Thank you for the patch.

Why the magic number instead of VK_MENU?

I think the condition can be like the following:

            if (ir.EventType == KEY_EVENT &&
                (ir.Event.KeyEvent.bKeyDown ||
                 ir.Event.KeyEvent.wVirtualKeyCode == VK_MENU) &&
                ir.Event.KeyEvent.uChar.UnicodeChar) {

[YO4]

I was concerned about VK_MENU having a different name than the ALT key, but VK_MENU is widely used.
Nevertheless, VK_MENU /* ALT key */ was better than using a magic number.
(And it's more kindness to non windows programmer. but of cource, there are already many Windows specific manner in codes)

In the next code,
It seems to GetConsoleInput() not generate (bKeyDown, VK_MENU, UnicodeChar != 0),
and I once considered a similar code, but it depends on that Windows behavior and I avoid it.
so my code is like this

            if (ir.EventType == KEY_EVENT &&
                (ir.Event.KeyEvent.bKeyDown ||
                 (!ir.Event.KeyEvent.bKeyDown && ir.Event.KeyEvent.wVirtualKeyCode == VK_MENU))
                ir.Event.KeyEvent.uChar.UnicodeChar) {
                ret = 1;
            }

I thought it was a bit confusing and two conditions represents different situation.
So I want to leave it straightforward and let the compiler handle it.
Which code style would you prefer?

[YO4]

modified proposal here.

            if (ir.EventType == KEY_EVENT && ir.Event.KeyEvent.uChar.UnicodeChar &&
                (ir.Event.KeyEvent.bKeyDown ||
                !ir.Event.KeyEvent.bKeyDown && ir.Event.KeyEvent.wVirtualKeyCode == VK_MENU)) {
                ret = 1;
            }

This includes all conditions, I think.
If it looks good, I would like to commit.

[nobu]

Either is ok.