Get next n object bytes

        Entry:
          AH = 12h
          BH = 12h
          BL = object
               00h handle is DWORD on top of stack
               01h read next N chars/attributes on task's default window
          STACK: DWORD count

        Return:
          STACK: DWORD width of screen line
                 DWORD address
                 DWORD count actually read