...when panel title has focus and space key is pressed

Fixes sidebar panel title decoration expand/collapse bitmap not updating
when keyboard space key is pressed. This has been present since at least
ver 5.1.6.2. Seems trival enough to not have go through the report
process. May be why I could find no bug report for it :-)

Change-Id: I7c0dfe511a780eb2bdc5ab8d1064549645cc30ae
Reviewed-on: https://gerrit.libreoffice.org/59680
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>