[aggResponse/hierarchical] prevent error when there are no 'split slices'
[aggResponse/hierarchicalData] test to prove 6bcf9aa
Merge branch 'master' into split_dat_pie

Conflicts:
	src/kibana/components/agg_response/hierarchical/build_hierarchical_data.js
Merge pull request #2221 from spenceralger/split_dat_pie

Prevent failure in Hierarchical converter