Restore terminal monitor attributes - addition

Patch 2d753894c7553d6a05e8fdbed5f4704398919a35 was missing this check,
when running monitor as /dev/tty and other serial device, i.e:
  qemu -monitor /dev/tty -serial /dev/pts/1

Without this patch any serial device will override the monitor stored
attributes. (monitor is called in main() before any serial device).

Signed-off-by: Shahar Havivi <shaharh@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
