DeskTop: Remove seemingly unneeded safety check when adjusting ports

When drawing window entries, the grafport needs to be adjusted to
account for the header. This is normally done in
`OffsetWindowGrafportAndSet` which updates the previously selected
`window_grafport`. Notably, while callers must be sensitive to
GetWinPort failing if the window is obscured, when the port is updated
and SetPort is called there is no subsequent check that the port is
not offscreen. MGTK seems okay with this.

When update events are being processed, a different grafport is
provided via `BeginUpdate`. This is clipped to just the necessary
update rect, e.g. what was revealed by a window move. There was
separate code to deal with updating the port to account for the header
here. And notably, because of issue #369, there was logic to ensure
the updated port was not offscreen. Why is it needed for updates, but
not for the normal drawing? Further testing reveals that the bug no
longer reproduces with this logic removed; likely it was only present
in old code that didn't use the grafport provided with the
`BeginUpdate`.

So... remove the check? Seems okay so far.

desktop/lc.s

@@ -148,7 +148,7 @@ params:  .res    3
         dey
         bpl     :-
 
-        ;; Determine the update's maprect is already below the header; if
+        ;; Determine if the update's maprect is already below the header; if
         ;; not, we need to offset the maprect below the header.
         sub16   desktop_grafport+MGTK::GrafPort::viewloc+MGTK::Point::ycoord, window_grafport+MGTK::GrafPort::viewloc+MGTK::Point::ycoord, tmpw
         scmp16  tmpw, #kWindowHeaderHeight
@@ -158,11 +158,6 @@ params:  .res    3
         add16 window_grafport+MGTK::GrafPort::viewloc+MGTK::Point::ycoord, #kWindowHeaderHeight, desktop_grafport+MGTK::GrafPort::viewloc+MGTK::Point::ycoord
         add16 window_grafport+MGTK::GrafPort::maprect+MGTK::Rect::y1, #kWindowHeaderHeight, desktop_grafport+MGTK::GrafPort::maprect+MGTK::Rect::y1
 
-        ;; MGTK doesn't like offscreen grafports, so if we end up with
-        ;; nothing to draw, skip drawing!
-        ;; https://github.com/a2stuff/a2d/issues/369
-        scmp16  desktop_grafport+MGTK::GrafPort::viewloc + MGTK::Point::ycoord, #kScreenHeight
-        bpl     fail
         MGTK_CALL MGTK::SetPort, desktop_grafport
         bne     fail