Don't return variant/text tracks before playhead

getVariantTracks and getTextTracks both check values on
player.playhead_, but don't check if the playhead exists beforehand.
This leads to problems when casting an encrypted asset; the cast status
update will check getVariantTracks and getTextTracks before the
playhead exists, and the error will make the status updates stop
coming.

Issue #1128

Change-Id: If38e586b1ea3006c01d3556216f5333d9eaf6e17

lib/player.js

@@ -1287,7 +1287,7 @@ shaka.Player.prototype.cancelTrickPlay = function() {
  * @export
  */
 shaka.Player.prototype.getVariantTracks = function() {
-  if (!this.manifest_)
+  if (!this.manifest_ || !this.playhead_)
     return [];
   this.assertCorrectActiveStreams_();
 
@@ -1312,7 +1312,7 @@ shaka.Player.prototype.getVariantTracks = function() {
  * @export
  */
 shaka.Player.prototype.getTextTracks = function() {
-  if (!this.manifest_)
+  if (!this.manifest_ || !this.playhead_)
     return [];
   this.assertCorrectActiveStreams_();
 

test/player_unit.js

@@ -1349,6 +1349,31 @@ describe('Player', function() {
       expect(player.getTextTracks()).toEqual(textTracks);
     });
 
+    it('returns empty arrays before tracks can be determined', function(done) {
+      var parser = new shaka.test.FakeManifestParser(manifest);
+      var parserFactory = function() { return parser; };
+      parser.start.and.callFake(function(manifestUri, playerInterface) {
+        // The player does not yet have a manifest.
+        expect(player.getVariantTracks()).toEqual([]);
+        expect(player.getTextTracks()).toEqual([]);
+
+        parser.playerInterface = playerInterface;
+        return Promise.resolve(manifest);
+      });
+      drmEngine.init.and.callFake(function(manifest, isOffline) {
+        // The player does not yet have a playhead.
+        expect(player.getVariantTracks()).toEqual([]);
+        expect(player.getTextTracks()).toEqual([]);
+      });
+
+      player.load('', 0, parserFactory).catch(fail).then(function() {
+        // Make sure the interruptions didn't mess up the tracks.
+        streamingEngine.onCanSwitch();
+        expect(player.getVariantTracks()).toEqual(variantTracks);
+        expect(player.getTextTracks()).toEqual(textTracks);
+      }).then(done);
+    });
+
     it('doesn\'t disable AbrManager if switching variants', function() {
       streamingEngine.onCanSwitch();