tdf#119527 Fix focus hidden by mouse click panel collapse

Set focus to the clicked panel title

Change-Id: I65993a6a2f8e7a9a2bdaa6cf4527d5b163d81409
Reviewed-on: https://gerrit.libreoffice.org/59694
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

sfx2/source/sidebar/PanelTitleBar.cxx

@@ -183,6 +183,7 @@ void PanelTitleBar::MouseButtonUp (const MouseEvent& rMouseEvent)
             {
                 mpPanel->SetExpanded( ! mpPanel->IsExpanded());
                 Invalidate();
+                GrabFocus();
             }
         }
     }