Update src/pointers.js

Co-authored-by: Mike Bostock <mbostock@gmail.com>

src/pointers.js

@@ -4,7 +4,7 @@ import sourceEvent from "./sourceEvent.js";
 export default function(events, node) {
   if (events.target) { // i.e., instanceof Event, not TouchList or iterable
     events = sourceEvent(events);
-    if (!node) node = events.currentTarget;
+    if (node === undefined) node = events.currentTarget;
     events = events.touches || [events];
   }
   return Array.from(events, event => pointer(event, node));