Get object eof status

        Entry:
          AH = 12h
          BH = 10h
          BL = object
               00h handle is DWORD on top of stack
               01h returns TRUE if logical cursor past end of task's def window
               02h return ??? for task's mailbox (task's handle on top of stack)
               03h return ??? for current task's mailbox

        Return:
          DWORD on top of stack is status