Only get types once in mergeArrays

Make a max of 2 calls to exports.getType instead of 4 calls.

Author: timtucker

dist/knockout.mapping.js

@@ -253,13 +253,18 @@
     }
 
     function mergeArrays(a, b) {
-        if (exports.getType(a) !== "array") {
-            if (exports.getType(a) === "undefined") a = [];
-            else a = [a];
+        if (a === undefined) {
+            a = [];
         }
-        if (exports.getType(b) !== "array") {
-            if (exports.getType(b) === "undefined") b = [];
-            else b = [b];
+        else if (exports.getType(a) !== "array") {
+            a = [a];
+        }
+
+        if (b === undefined) {
+            b = [];
+        }
+        else if (exports.getType(b) !== "array") {
+            b = [b];
         }
 
         return ko.utils.arrayGetDistinctValues(a.concat(b));