CLJS-255: fix counting LazySeq

(count (lazy-seq nil)) now correctly evaluates to 0.

src/cljs/cljs/core.cljs

@@ -606,18 +606,19 @@ reduces them without incurring seq initialization"
 
 (declare counted?)
 
-(defn- accumulating-seq-count [coll acc]
-  (if (counted? coll) ; assumes nil is counted, which it currently is
-    (+ acc (-count coll))
-    (recur (next coll) (inc acc))))
+(defn- accumulating-seq-count [coll]
+  (loop [s (seq coll) acc 0]
+    (if (counted? s) ; assumes nil is counted, which it currently is
+      (+ acc (-count s))
+      (recur (next s) (inc acc)))))
 
 (defn count
   "Returns the number of items in the collection. (count nil) returns
   0.  Also works on strings, arrays, and Maps"
   [coll]
   (if (counted? coll)
     (-count coll)
-    (accumulating-seq-count coll 0)))
+    (accumulating-seq-count coll)))
 
 (declare indexed?)