Shaders generated from shader graphs are incomplete with some layer combinations

Given this graph:

      _      _edge0i_ function0 _edge0o_
{{     /                              }}
{{ input                                output}}
     _edge1i__ function1 _edge1o_/

with function0 and edge0o on layer "0" only
 and function1 and edge1o on layer "1" only
 and all other nodes and edges on all layers.

The QShaderGraph class fails to to generate statements with enabledLayers = {"0"}.

The issue is that when only layer "1" is disabled, edge1i doesn't get properly discarded and Kahn's algorithm doesn't ever schedule input.