Empty facet domain causes rendering errors

[mbostock]

Looks like we don’t handle this case very gracefully:

Plot.rectY([], { x: "date", y: "visitors", fy: "path" }).plot()

From the console:

Error: <svg> attribute height: Expected length, "NaN".
Error: <svg> attribute viewBox: Expected number, "0 0 640 NaN".
Error: <text> attribute transform: Trailing garbage, "translate(600,NaN) rotate(-90)".
Error: <text> attribute transform: Trailing garbage, "translate(40,undefined)".
Error: <text> attribute transform: Trailing garbage, "translate(600,NaN)".