fix C# test access violation exception on Windows

src/core/iomgr/resolve_address_windows.c

@@ -135,9 +135,9 @@ static void do_request(void *rp) {
   grpc_resolve_cb cb = r->cb;
   gpr_free(r->name);
   gpr_free(r->default_port);
+  grpc_iomgr_unregister_object(&r->iomgr_object);
   gpr_free(r);
   cb(arg, resolved);
-  grpc_iomgr_unregister_object(&r->iomgr_object);
 }
 
 void grpc_resolved_addresses_destroy(grpc_resolved_addresses *addrs) {

src/core/iomgr/socket_windows.c

@@ -85,13 +85,13 @@ int grpc_winsocket_shutdown(grpc_winsocket *socket) {
    both memory and sockets. */
 void grpc_winsocket_orphan(grpc_winsocket *winsocket) {
   SOCKET socket = winsocket->socket;
+  grpc_iomgr_unregister_object(&winsocket->iomgr_object);
   if (winsocket->read_info.outstanding || winsocket->write_info.outstanding) {
     grpc_iocp_socket_orphan(winsocket);
   } else {
     grpc_winsocket_destroy(winsocket);
   }
   closesocket(socket);
-  grpc_iomgr_unregister_object(&winsocket->iomgr_object);
 }
 
 void grpc_winsocket_destroy(grpc_winsocket *winsocket) {