fix output_array_stats() for empty arrays
fix output_array_stats() for empty arrays

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