fdo#71248 Excel VBA: ActiveDocument is not tracking currently selected Doc

Change-Id: I86606646206ec26e2822a6e27888537d44351b7b
Reviewed-on: https://gerrit.libreoffice.org/11725
Reviewed-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>
Tested-by: Samuel Mehrbrodt <s.mehrbrodt@gmail.com>