Fix #1155 for d3.geom.quadtree.

component.json

 {
   "name": "d3",
-  "version": "3.1.1",
+  "version": "3.1.2",
   "main": "./d3.js"
 }

d3.js

 d3 = function() {
   var d3 = {
-    version: "3.1.1"
+    version: "3.1.2"
   };
   if (!Date.now) Date.now = function() {
     return +new Date();
@@ -4491,6 +4491,7 @@ d3 = function() {
         x1_ = x1, y1_ = y1, x2_ = x2, y2_ = y2;
       } else {
         x2_ = y2_ = -(x1_ = y1_ = Infinity);
+        xs = [], ys = [];
         n = data.length;
         if (compat) for (i = 0; i < n; ++i) {
           d = data[i];

package.json

 {
   "name": "d3",
-  "version": "3.1.1",
+  "version": "3.1.2",
   "description": "A small, free JavaScript library for manipulating documents based on data.",
   "keywords": [
     "dom",

src/geom/quadtree.js

@@ -37,6 +37,7 @@ d3.geom.quadtree = function(points, x1, y1, x2, y2) {
     } else {
       // Compute bounds, and cache points temporarily.
       x2_ = y2_ = -(x1_ = y1_ = Infinity);
+      xs = [], ys = [];
       n = data.length;
       if (compat) for (i = 0; i < n; ++i) {
         d = data[i];

src/start.js

 d3 = (function(){
-  var d3 = {version: "3.1.1"}; // semver
+  var d3 = {version: "3.1.2"}; // semver