fix(query): pass projection fields to cursor

Fix #4342

lib/query.js

@@ -2873,6 +2873,7 @@ Query.prototype.stream = util.deprecate(Query.prototype.stream, 'Mongoose: ' +
 Query.prototype.cursor = function cursor(opts) {
   this._applyPaths();
   this._fields = this._castFields(this._fields);
+  this.setOptions({ fields: this._fieldsForExec() });
   if (opts) {
     this.setOptions(opts);
   }

test/query.cursor.test.js

@@ -72,6 +72,35 @@ describe('QueryCursor', function() {
       });
     });
 
+    it('with projection', function(done) {
+      var personSchema = new Schema({
+        name: String,
+        born: String
+      });
+      var Person = db.model('Person4342', personSchema);
+      var people = [
+        { name: 'Axl Rose', born: 'William Bruce Rose' },
+        { name: 'Slash', born: 'Saul Hudson' }
+      ];
+      Person.create(people, function(error) {
+        assert.ifError(error);
+        var cursor = Person.find({}, { _id: 0, name: 1 }).sort({ name: 1 }).cursor();
+        cursor.next(function(error, doc) {
+          assert.ifError(error);
+          assert.equal(doc._id, undefined);
+          assert.equal(doc.name, 'Axl Rose');
+          assert.equal(doc.born, undefined);
+          cursor.next(function(error, doc) {
+            assert.ifError(error);
+            assert.equal(doc._id, undefined);
+            assert.equal(doc.name, 'Slash');
+            assert.equal(doc.born, undefined);
+            done();
+          });
+        });
+      });
+    });
+
     it('with populate', function(done) {
       var bandSchema = new Schema({
         name: String,