Fix element.click() sending tap on IE10

IE 10 uses current mouse position for clientX and clientY, which breaks the
TAP_DISTANCE function.
Use NaN as a default start position to mitigate

Fixes #1640 [1.0] Tap gesture does not trigger when calling `this.click` in IE10

src/standard/gestures.html

@@ -411,12 +411,12 @@
     deps: ['mousedown', 'click', 'touchstart', 'touchend'],
     emits: ['tap'],
     start: {
-      x: 0,
-      y: 0
+      x: NaN,
+      y: NaN
     },
     reset: function() {
-      this.start.x = 0;
-      this.start.y = 0;
+      this.start.x = NaN;
+      this.start.y = NaN;
     },
     save: function(e) {
       this.start.x = e.clientX;