fix Mesh.localize() for empty element groups
fix Mesh.localize() for empty element groups

vlukes/sfepy,rc/sfepy,sfepy/sfepy,lokik/sfepy,vlukes/sfepy,rc/sfepy,lokik/sfepy,rc/sfepy,RexFuzzle/sfepy,vlukes/sfepy,RexFuzzle/sfepy,sfepy/sfepy,lokik/sfepy,BubuLK/sfepy,BubuLK/sfepy,RexFuzzle/sfepy,lokik/sfepy,sfepy/sfepy,BubuLK/sfepy,RexFuzzle/sfepy