avoid scrolling too far for scroll-via-copy

But scroll-via-copy is still not enabled.

gui-lib/mred/private/wxme/editor-canvas.rkt

@@ -981,7 +981,8 @@
             (let-boxes ([fx 0]
                         [old-fy 0]
                         [new-fy 0])
-                (begin
+                (let ([x (min x scroll-width)]
+                      [y (min y scroll-height)])
                   (convert-scroll-to-location x y fx new-fy)
                   (convert-scroll-to-location old-x old-y #f old-fy))
               (let-boxes ([vx 0][vy 0][vw 0][vh 0])