fix Region.get_cell_indices() for no common cells
fix Region.get_cell_indices() for no common cells

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