Do not close fd 2 if it's the one we need

This should not happen based if stderr was not already closed,
but it's better not to make assumptions.

dispvm/qubes-restore.c

@@ -465,6 +465,8 @@ void redirect_stderr(void)
 		exit(1);
 	}
 	dup2(fd, 2);
+	if (fd != 2)
+		close(fd);
 }