d3.bin should check for null

[mbostock]

Our threshold implementations do already, which is good (via count), but we shouldn’t be passing null values in here:

d3-array/src/bin.js

Lines 80 to 82 in 6fda277

	if (x0 <= x && x <= x1) {
	bins[bisect(tz, x, 0, m)].push(data[i]);
	}

(Undefined and NaN values already fail this test, so we’re good on those.)