sw: fix ASAN detected error in RtfSdrExport::Commit()
sw: fix ASAN detected error in RtfSdrExport::Commit()

EscherPropertyContainer may allocate a 1-byte buffer if there are no
vertices / segments. (happens in sw_filters_test)

 in EscherPropertyContainer::CreateCustomShapeProperties(MSO_SPT, com::sun::star::uno::Reference<com::sun::star::drawing::XShape> const&) filter/source/msfilter/escherex.cxx:3853:25

Change-Id: I56dedbd57d38cd017183060e924cb1340ea58ebf

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core