Fix data_grammar_from_schema for empty cases
Fix data_grammar_from_schema for empty cases

* src/lib/yang/data.lua (data_grammar_from_schema): Prune cases with no
  members.  Can be the case when we're asking for state data, for
  example, and a case has no state data.

dpino/snabbswitch,SnabbCo/snabbswitch,eugeneia/snabbswitch,eugeneia/snabbswitch,Igalia/snabb,eugeneia/snabb,Igalia/snabb,alexandergall/snabbswitch,alexandergall/snabbswitch,Igalia/snabbswitch,eugeneia/snabb,eugeneia/snabbswitch,snabbco/snabb,alexandergall/snabbswitch,alexandergall/snabbswitch,Igalia/snabb,Igalia/snabbswitch,alexandergall/snabbswitch,Igalia/snabb,dpino/snabbswitch,snabbco/snabb,Igalia/snabbswitch,snabbco/snabb,snabbco/snabb,alexandergall/snabbswitch,dpino/snabb,dpino/snabbswitch,eugeneia/snabb,snabbco/snabb,dpino/snabb,eugeneia/snabb,Igalia/snabb,eugeneia/snabbswitch,Igalia/snabb,Igalia/snabbswitch,dpino/snabb,Igalia/snabb,snabbco/snabb,dpino/snabbswitch,snabbco/snabb,SnabbCo/snabbswitch,dpino/snabb,alexandergall/snabbswitch,eugeneia/snabb,alexandergall/snabbswitch,SnabbCo/snabbswitch,dpino/snabb,dpino/snabb,Igalia/snabbswitch,dpino/snabb,eugeneia/snabb,snabbco/snabb,eugeneia/snabb,eugeneia/snabb,SnabbCo/snabbswitch,Igalia/snabb