Ensure that the first point for kinetic is valid

src/ol/kinetic.js

@@ -81,25 +81,30 @@ ol.Kinetic.prototype.update = function(x, y) {
  * @return {boolean} Whether we should do kinetic animation.
  */
 ol.Kinetic.prototype.end = function() {
+  if (this.points_.length < 6) {
+    // at least 2 points are required (i.e. there must be at least 6 elements
+    // in the array)
+    return false;
+  }
   var delay = goog.now() - this.delay_;
   var lastIndex = this.points_.length - 3;
   if (this.points_[lastIndex + 2] < delay) {
-    // the user stopped panning before releasing the map
+    // the last tracked point is too old, which means that the user stopped
+    // panning before releasing the map
     return false;
   }
+
+  // get the first point which still falls into the delay time
   var firstIndex = lastIndex - 3;
-  while (firstIndex >= 0 && this.points_[firstIndex + 2] > delay) {
+  while (firstIndex > 0 && this.points_[firstIndex + 2] > delay) {
     firstIndex -= 3;
   }
-  if (firstIndex >= 0) {
+  var duration = this.points_[lastIndex + 2] - this.points_[firstIndex + 2];
-    var duration = this.points_[lastIndex + 2] - this.points_[firstIndex + 2];
+  var dx = this.points_[lastIndex] - this.points_[firstIndex];
-    var dx = this.points_[lastIndex] - this.points_[firstIndex];
+  var dy = this.points_[lastIndex + 1] - this.points_[firstIndex + 1];
-    var dy = this.points_[lastIndex + 1] - this.points_[firstIndex + 1];
+  this.angle_ = Math.atan2(dy, dx);
-    this.angle_ = Math.atan2(dy, dx);
+  this.initialVelocity_ = Math.sqrt(dx * dx + dy * dy) / duration;
-    this.initialVelocity_ = Math.sqrt(dx * dx + dy * dy) / duration;
+  return this.initialVelocity_ > this.minVelocity_;
-    return this.initialVelocity_ > this.minVelocity_;
-  }
-  return false;
 };