Fixed error: attempt to divide by (void) when axis bounds' length is a multiple of 1000

Please merge into 5.2

collects/plot/common/ticks.rkt

@@ -31,7 +31,7 @@
     (define step (let ([y  (/ (- x-max x-min) mag)])
                    (cond [(y . < . 2)  (* 1/5 mag)]
                          [(y . < . 5)  (* 1/2 mag)]
-                         [(y . < . 10)  mag])))
+                         [else         mag])))
     (define start (* (ceiling (/ x-min step)) step))
     (define stop (* (floor (/ x-max step)) step))
     (define num (+ 1 (round (/ (- stop start) step))))

collects/plot/tests/plot2d-tests.rkt

@@ -11,6 +11,8 @@
 
 (plot empty #:x-min -1 #:x-max 1 #:y-min -1 #:y-max 1)
 
+(time (plot (function values 0 1000)))
+
 (parameterize ([plot-background  "black"]
                [plot-foreground  "white"]
                [plot-background-alpha  1/2]