JS stack trace when copying characters

[Olivier Tilloy]

No crash or loss of functionality, but I noticed numerous JS stack traces being printed when I ran gnome-characters from a terminal, and copied a character, they all look like that:

(org.gnome.Characters:1204): Gjs-CRITICAL **: 15:46:20.767: Object .Gjs_CharacterDialog (0x55d686b90600), has been already finalized. Impossible to get any property from it.
== Stack trace for context 0x55d685fa20b0 ==
#0 0x7ffc4c56fd80 I resource:///org/gnome/gjs/modules/_legacy.js:80 (0x7f6ac3ec0670 @ 26)
#1 0x7ffc4c570540 b self-hosted:917 (0x7f6ac3ee5450 @ 394)
#2 0x55d6861da0c8 i resource:///org/gnome/Characters/js/main.js:112 (0x7f6ac3ed52b8 @ 37)
#3 0x55d6861da038 i resource:///org/gnome/gjs/modules/package.js:221 (0x7f6ac3e86f78 @ 45)
#4 0x55d6861d9fb8 i /usr/bin/gnome-characters:6 (0x7f6ac3e86b38 @ 53)

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gnome-characters 3.26.2-4
ProcVersionSignature: Ubuntu 4.15.0-10.11-generic 4.15.3
Uname: Linux 4.15.0-10-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.8-0ubuntu10
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Tue Feb 27 15:47:07 2018
EcryptfsInUse: Yes
InstallationDate: Installed on 2016-07-02 (604 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
SourcePackage: gnome-characters
UpgradeStatus: Upgraded to bionic on 2018-01-29 (29 days ago)