CLJS-459: fix reduce-kv node visit order for sorted maps

Includes a basic test.

src/cljs/cljs/core.cljs

@@ -5030,12 +5030,12 @@ reduces them without incurring seq initialization"
     (throw (js/Error. "red-black tree invariant violation"))))
 
 (defn- tree-map-kv-reduce [node f init]
-  (let [init (f init (.-key node) (.-val node))]
+  (let [init (if-not (nil? (.-left node))
+               (tree-map-kv-reduce (.-left node) f init)
+               init)]
     (if (reduced? init)
       @init
-      (let [init (if-not (nil? (.-left node))
-                   (tree-map-kv-reduce (.-left node) f init)
-                   init)]
+      (let [init (f init (.-key node) (.-val node))]
         (if (reduced? init)
           @init
           (let [init (if-not (nil? (.-right node))

test/cljs/cljs/core_test.cljs

@@ -1773,6 +1773,10 @@
     (let [x (fn [] "overwritten")]
       (assert (= "original" (y)))))
 
+  ;; CLJS-459: reduce-kv visit order
+  (assert (= (reduce-kv conj [] (sorted-map :foo 1 :bar 2))
+             [:bar 2 :foo 1]))
+
   ;; Test builtin implementations of IKVReduce
   (letfn [(kvr-test [data expect]
             (assert (= :reduced (reduce-kv (fn [_ _ _] (reduced :reduced))