Calling update() breaks circular link paths

[antoinerg]

First of all, thank you for this very nice library @ricklupton

I have seen a strange behavior when using update: when calling sankey.update(graph) with an unmodified graph object, circular links (usually made out of 4 segments) are now made out of 2 segments.

The layout goes from:

to the following wrong result upon calling update:

Programmatically, this can be seen by running the following:

            var graph = sankey(data);
            var before = graph.links.map(function(link) {
                return link.points.map(function(pts) {
                    return pts.d;
                });
            });
            console.log(before);
            // [['r', 'r'], ['r', 'r', 'r', 'r'], ['r', 'r'], ['r', 'r'], ['r', 'l', 'l', 'r'], ['r', 'r'], ['r', 'l', 'l', 'r']]

            graph = sankey.update(graph);
            var after = graph.links.map(function(link) {
              return link.points.map(function(pts) {
                  return pts.d;
              });
            });
            console.log(after);
            // [['r', 'r'], ['r', 'r'], ['r', 'r'], ['r', 'r'], ['r', 'r'], ['r', 'r'], ['r', 'r']]