which adds the problem that GtkComboBox doesn't send a focus-in,
but its toggle does, to find and use that instead

Change-Id: I18d46511bf2e6997539a8413f574a94b24b4583f
Reviewed-on: https://gerrit.libreoffice.org/67136
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>