Ensure _.merge skips merging when object and source are the same value.

lodash.js

@@ -2529,6 +2529,9 @@
      * @param {Array} [stackB=[]] Associates values with source counterparts.
      */
     function baseMerge(object, source, customizer, stackA, stackB) {
+      if (object === source) {
+        return;
+      }
       var props = (isArray(source) || isTypedArray(source)) ? undefined : keysIn(source);
       arrayEach(props || source, function(srcValue, key) {
         if (props) {

test/test.js

@@ -12293,6 +12293,28 @@
       assert.deepEqual(actual, expected);
     });
 
+    QUnit.test('should skip merging when `object` and `source` are the same value', function(assert) {
+      assert.expect(1);
+
+      if (defineProperty) {
+        var object = {},
+            pass = true;
+
+        defineProperty(object, 'a', {
+          'enumerable': true,
+          'configurable': true,
+          'get': function() { pass = false; },
+          'set': function() { pass = false; }
+        });
+
+        _.merge(object, object);
+        assert.ok(pass);
+      }
+      else {
+        skipTest(assert);
+      }
+    });
+
     QUnit.test('should convert values to arrays when merging with arrays of `source`', function(assert) {
       assert.expect(2);