Ensure map and set clones contain custom properties of source values. [closes #3951]

lodash.js

@@ -2671,16 +2671,10 @@
         value.forEach(function(subValue) {
           result.add(baseClone(subValue, bitmask, customizer, subValue, value, stack));
         });
-
-        return result;
-      }
-
-      if (isMap(value)) {
+      } else if (isMap(value)) {
         value.forEach(function(subValue, key) {
           result.set(key, baseClone(subValue, bitmask, customizer, key, value, stack));
         });
-
-        return result;
       }
 
       var keysFunc = isFull