fix dask_single, dask_threads backends in ETermBase.make_function()
fix dask_single, dask_threads backends in ETermBase.make_function()

- automatic chunk sizes smaller that whole arrays work

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