fix slice mode offsets in compose_sparse()
fix slice mode offsets in compose_sparse()

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