mingw: adjust is_console() to work with stdin

When determining whether a handle corresponds to a *real* Win32 Console
(as opposed to, say, a character device such as /dev/null), we use the
GetConsoleOutputBufferInfo() function as a tell-tale.

However, that does not work for *input* handles associated with a
console. Let's just use the GetConsoleMode() function for input handles,
and since it does not work on output handles fall back to the previous
method for those.

This patch prepares for using is_console() instead of my previous
misguided attempt in cbb3f3c (mingw: intercept isatty() to handle
/dev/null as Git expects it, 2016-12-11) that broke everything on
Windows.

Signed-off-by: Johannes Schindelin <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: dscho

compat/winansi.c

@@ -84,6 +84,7 @@ static void warn_if_raster_font(void)
 static int is_console(int fd)
 {
 	CONSOLE_SCREEN_BUFFER_INFO sbi;
+	DWORD mode;
 	HANDLE hcon;
 
 	static int initialized = 0;
@@ -98,7 +99,10 @@ static int is_console(int fd)
 		return 0;
 
 	/* check if its a handle to a console output screen buffer */
-	if (!GetConsoleScreenBufferInfo(hcon, &sbi))
+	if (!fd) {
+		if (!GetConsoleMode(hcon, &mode))
+			return 0;
+	} else if (!GetConsoleScreenBufferInfo(hcon, &sbi))
 		return 0;
 
 	/* initialize attributes */