Define navigator.maxTouchPoints as 0 when unknown

Fixes gh-332
Closes gh-335

README.md

@@ -102,7 +102,7 @@ Touches will not generate events unless inside of an area that has a valid `touc
 
 ## navigator.maxTouchPoints
 
-As the information necessary to populate [`navigator.maxTouchPoints`](https://www.w3.org/TR/pointerevents/#extensions-to-the-navigator-interface) is not available in browsers that do not natively implement pointer events, PEP does not currently polyfill this extension to the `navigator` interface.
+As the information necessary to populate [`navigator.maxTouchPoints`](https://www.w3.org/TR/pointerevents/#extensions-to-the-navigator-interface) is not available in browsers that do not natively implement pointer events, PEP sets the value to `0`, which is "the minimum number guaranteed to be recognized" as required by the specification.
 
 ### Browser Compatibility
 

src/platform-events.js

@@ -18,6 +18,10 @@ export function applyPolyfill() {
       });
       dispatcher.registerSource('ms', msEvents);
     } else {
+      Object.defineProperty(window.navigator, 'maxTouchPoints', {
+        value: 0,
+        enumerable: true
+      });
       dispatcher.registerSource('mouse', mouseEvents);
       if (window.ontouchstart !== undefined) {
         dispatcher.registerSource('touch', touchEvents);