webglapp: ensure that neurons without inputs or outputs don't incur in errors when shading them by Signal flow centrality.
webglapp: ensure that neurons without inputs or outputs don't incur in errors
when shading them by Signal flow centrality.

fzadow/CATMAID,htem/CATMAID,htem/CATMAID,fzadow/CATMAID,fzadow/CATMAID,htem/CATMAID,fzadow/CATMAID,htem/CATMAID