script: make it work even if fd 0 is closed

Testcase:
script -q -c "echo hey" /dev/null 0>&-

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

util-linux/script.c

@@ -77,8 +77,15 @@ int script_main(int argc UNUSED_PARAM, char **argv)
 	if (!(opt & OPT_q)) {
 		printf("Script started, file is %s\n", fname);
 	}
+
 	shell = get_shell_name();
 
+	/* Some people run "script ... 0>&-".
+	 * Our code assumes that STDIN_FILENO != pty.
+	 * Ensure STDIN_FILENO is not closed:
+	 */
+	bb_sanitize_stdio();
+
 	pty = xgetpty(pty_line);
 
 	/* get current stdin's tty params */