use single cell dummy material in DotProductVolumeTerm.get_fargs()
use single cell dummy material in DotProductVolumeTerm.get_fargs()

vlukes/sfepy,BubuLK/sfepy,sfepy/sfepy,sfepy/sfepy,rc/sfepy,BubuLK/sfepy,rc/sfepy,vlukes/sfepy,BubuLK/sfepy,vlukes/sfepy,sfepy/sfepy,rc/sfepy