Fix propery name duplication check in case of empty collection (#4098)

Fixes: #4093

JerryScript-DCO-1.0-Signed-off-by: Peter Gal pgal.usz@partner.samsung.com

tests/jerry/es.next/regression-test-issue-4093.js

@@ -0,0 +1,25 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+var v138 = {
+    ownKeys: function() { return []; },
+};
+
+var v140 = new Proxy ({}, v138);
+
+/* expected an empty array */
+var result = Object.getOwnPropertyNames (v140);
+
+assert (result instanceof Array);
+assert (result.length === 0);