Risk of divide by zero

[bjornharrtell]

At

flatbush/index.js

Lines 130 to 131 in a71e9a5

	const x = Math.floor(hilbertMax * ((minX + maxX) / 2 - this.minX) / width);
	const y = Math.floor(hilbertMax * ((minY + maxY) / 2 - this.minY) / height);

width or height could be zero.