mingw: consider that UNICODE_STRING::Length counts bytes

UNICODE_STRING::Length field means size of buffer in bytes[1], despite
of buffer itself being array of wchar_t. Because of that terminating
zero is placed twice as far. Fix it.

[1] https://msdn.microsoft.com/en-us/library/windows/desktop/aa380518.aspx

Signed-off-by: Max Kirillov <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>

Author: max630

compat/winansi.c

@@ -638,7 +638,7 @@ static void detect_msys_tty(int fd)
 			buffer, sizeof(buffer) - 2, &result)))
 		return;
 	name = nameinfo->Name.Buffer;
-	name[nameinfo->Name.Length] = 0;
+	name[nameinfo->Name.Length / sizeof(*name)] = 0;
 
 	/*
 	 * Check if this could be a MSYS2 pty pipe ('msys-XXXX-ptyN-XX')