fix surface region case in extend_cell_data()
fix surface region case in extend_cell_data()

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