Crash on WNT in CppunitTest_sw_globalfilter testSkipImages()

SfxBaseModel::dispose() calls some event listener that deletes the
BasicManager instance; unfortunately SfxObjectShell_Impl has a
SfxBasicHolder member that still refers to the deleted BasicManager
and then something calls vba::getVBAServiceFactory()...

Try to fix that by clearing the SfxBasicHolder member via SfxListener.

Change-Id: I65f2ec8e9eb598be218136c06ed8de35a464a971