Only set a target update time for live manifests.

Issue #21

Change-Id: I7bb43972b08f1121268ae5590bd5f456f97659ab

lib/player/dash_video_source.js

@@ -216,12 +216,11 @@ shaka.player.DashVideoSource.prototype.onStartStreams = function(
       'Initial seek range:',
       [this.seekStartTime_, this.seekEndTime_]);
 
-  // Set a target update time so we update the manifest before any Streams
-  // exhaust their SegmentIndexes.
-  this.setTargetUpdateTime_();
-
   this.fireSeekRangeChangedEvent_();
   if (this.manifestInfo.live) {
+    // Set a target update time so we update the manifest before any Streams
+    // exhaust their SegmentIndexes.
+    this.setTargetUpdateTime_();
     this.setSeekRangeUpdateTimer_();
   }
 };
@@ -372,6 +371,8 @@ shaka.player.DashVideoSource.prototype.setUpdateTimer_ = function(
  * @private
  */
 shaka.player.DashVideoSource.prototype.setTargetUpdateTime_ = function() {
+  shaka.asserts.assert(this.manifestInfo && this.manifestInfo.live);
+
   // Keep track of the the largest start time of the second last segment. We
   // want to update the manifest before the video's current time reaches the
   // last segment.