password verification fixes keyboard input source

[Konstantin Karandashev]

As the software updater requested admin password for verification, I could not change the keyboard input source from Cyrillic (Russian) to Latin (US). Manually switching to English in the text entry panel or deleting Russian from the list of available input sources led to "En" appearing in the panel, but the typing was still done in Russian throughout all open windows. The issue disappeared once the application was closed.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: software-properties-gtk 0.96.20.7
ProcVersionSignature: Ubuntu 4.4.0-127.153-generic 4.4.128
Uname: Linux 4.4.0-127-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.18
Architecture: amd64
CurrentDesktop: Unity
Date: Sun Jun 3 13:39:55 2018
EcryptfsInUse: Yes
InstallationDate: Installed on 2016-07-28 (675 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
PackageArchitecture: all
SourcePackage: software-properties
UpgradeStatus: No upgrade log present (probably fresh install)