fdo#72163 after updating m_xComposer, command facets are not dirty anymore

Else we dispose m_xComposer too eagerly; still used by m_pCacheSet.

Change-Id: I205488465c19a356534df17b8a5e9a20ce6766c9
Reviewed-on: https://gerrit.libreoffice.org/6906
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>