Fix demo app multi period stream track selection for downloading

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=199791722

demos/main/src/main/java/com/google/android/exoplayer2/demo/DownloadTracker.java

@@ -271,11 +271,11 @@ public class DownloadTracker implements DownloadManager.Listener {
             trackTitles.add(trackNameProvider.getTrackName(trackGroup.getFormat(k)));
             trackTitles.add(trackNameProvider.getTrackName(trackGroup.getFormat(k)));
           }
           }
         }
         }
-        if (!trackKeys.isEmpty()) {
-          builder.setView(dialogView);
-        }
-        builder.create().show();
       }
       }
+      if (!trackKeys.isEmpty()) {
+        builder.setView(dialogView);
+      }
+      builder.create().show();
     }
     }
 
 
     @Override
     @Override