fix rotate so that it can accept non-integral arguments

closes PR 12632

collects/2htdp/private/image-more.rkt

@@ -754,7 +754,7 @@
   (unless (and (<= 0 θ)
                (< θ 360))
     (error 'degrees->complex "~s" θ))
-  (case (modulo θ 360)
+  (case (and (integer? θ) (modulo θ 360))
     [(0)    1+0i]
     [(90)   0+1i]
     [(180) -1+0i]

collects/2htdp/tests/test-image.rkt

@@ -886,6 +886,11 @@
       =>
       #t)
 
+;; make sure rotate can get non-integral arguments
+(test (rotate -90.5 (rotate 90.5 (rectangle 20 100 'solid 'orange)))
+      =>
+      (rectangle 20 100 'solid 'orange))
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;
 ;; scaling tests