Generating key and confirmation dialog is not shown when creating PGP key

To reproduce:

 - Add GPG -> PGP key

Expected: shows the "Generating key" progress dialog (https://gitlab.gnome.org/GNOME/seahorse/blob/3.20.0/pgp/seahorse-gpgme-generate.c#L226) and a confirmation dialog to indicate key has been created successfully.

Actual: No dialog is shown during key generation or when key is created.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: seahorse 3.20.0-5
ProcVersionSignature: User Name 4.15.0-43.46-generic 4.15.18
Uname: Linux 4.15.0-43-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sun Dec 30 10:28:19 2018
EcryptfsInUse: Yes
InstallationDate: Installed on 2018-09-12 (108 days ago)
InstallationMedia: Ubuntu 16.04.5 LTS "Xenial Xerus" - Release amd64 (20180731)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: seahorse
UpgradeStatus: Upgraded to bionic on 2018-09-28 (92 days ago)