Fix property descriptor queries (#3840)

When the getOwnPropertyDescriptor method was invoked the input property
descriptor was not cleared in every case. This could lead to problems when
the property descriptor is not set/modified by the getOwnPropertyDescriptor
call, resulting in a failure at a later state.

Related to this the Proxy getOwnPropertyDescriptor method incorrectly returned
"undefined" value in a single case.

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

tests/jerry/es2015/regression-test-issue-3837.js

@@ -0,0 +1,33 @@
+// 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.
+
+function dummy ()
+{
+  "D" + "a";
+}
+
+var p1Handler = { getOwnPropertyDescriptor: dummy };
+var p1 = new Proxy({}, p1Handler);
+
+function dummyString ()
+{
+  return "a";
+}
+
+var p2Handler = { deleteProperty: dummyString };
+var p2 = new Proxy(p1, p2Handler);
+
+var result = (delete p2[1]);
+
+assert (result);