Button for changing input type outside of textfield does not work

Reproduce
==========
1) Open a File manager
2) Press the button for changing the input language ( on Japanese keyboards that's the `半角・全角・漢字` button below `ESC`.
3)
Expected: Input language changes
Actual: Input language does not change

Workaround
==========
- Click inside a random text field
- Press the button for changing input language

Why is this important?
======================
When navigating around the system, it's sometimes necessary to switch to English input without having a text field.

Consider this example
- Image you have an English file structure
- Set the input language to Japanese
- Open a file manager
- Search for a folder/file by starting to type
- You'll get gibberish because you're trying to write English with Japanese input. The file selection cursor might even jump to random position according to your input.
- Press `Esc` to try again in English.
- Press The language changing button
- Start typing again.
- You get gibberish again, because outside of the search field the language-changing button press was ignored.

lsb_release -rd
================
Description: Ubuntu 20.04.1 LTS
Release: 20.04

apt-cache policy
================
ibus-anthy:
  Installed: 1.5.11-1build1
  Candidate: 1.5.11-1build1
  Version table:
 *** 1.5.11-1build1 500
        500 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages
        100 /var/lib/dpkg/status

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ibus-anthy 1.5.11-1build1
ProcVersionSignature: Ubuntu 5.4.0-48.52-generic 5.4.60
Uname: Linux 5.4.0-48-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.9
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: XFCE
Date: Wed Sep 30 09:58:41 2020
SourcePackage: ibus-anthy
UpgradeStatus: Upgraded to focal on 2020-07-24 (67 days ago)