fix Bitmap%:get-argb-pixels type in images/flomap

- added missing case

closes PR 13717

collects/images/private/flomap.rkt

@@ -20,6 +20,8 @@
           [get-height (-> Integer)]
           [get-argb-pixels
            (case-> 
+            (Integer Integer Integer Integer Bytes
+                     -> Void)
             (Integer Integer Integer Integer Bytes Boolean
                      -> Void)
             (Integer Integer Integer Integer Bytes Boolean Boolean

collects/images/tests/other-tests.rkt

@@ -0,0 +1,20 @@
+#lang racket/gui
+(require images/flomap)
+
+(require rackunit)
+
+;; checks pr 13717
+
+(define bmp
+  (flomap->bitmap
+   (build-flomap 1 10 10
+                 (lambda (k x y) (/ (+ x y) 200)))))
+
+(define bmp-buf1 (make-bytes (* 10 10 4)))
+(define bmp-buf2 (make-bytes (* 10 10 4)))
+
+(send bmp get-argb-pixels 0 0 10 10 bmp-buf1)
+(send bmp set-argb-pixels 0 0 10 10 bmp-buf1)
+(send bmp get-argb-pixels 0 0 10 10 bmp-buf2)
+
+(check-equal? bmp-buf1 bmp-buf2)