Refactor a tiny bit of SwLayAction::IsShortCut

Change-Id: I13d4fbebec02bddaa27e8929188d497dde715730
Reviewed-on: https://gerrit.libreoffice.org/10980
Reviewed-by: Björn Michaelsen <bjoern.michaelsen@canonical.com>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>