raise error on negative printable width or height

quad/quadwriter/render.rkt

@@ -339,7 +339,10 @@
       (setup-margins qs page-width page-height))
     (define gutter-margin (and (pair? qs) (quad-ref (car qs) :page-margin-gutter 0)))
     (define printable-width (- page-width left-margin right-margin gutter-margin))
-    (define printable-height (- page-height top-margin bottom-margin))
+    (unless (> printable-width 0)
+      (raise-user-error 'render "printable width greater than 0: got ~a" printable-height))    (define printable-height (- page-height top-margin bottom-margin))
+    (unless (> printable-height 0)
+      (raise-user-error 'render "printable height greater than 0: got ~a" printable-height))
     (define column-count (setup-column-count qs))
     (define column-gap (setup-column-gap qs))
     (define line-wrap-size (/ (- printable-width (* (sub1 column-count) column-gap)) column-count))