Keep newly assigned window sequence number if queue is still empty.

When the queue is empty, we may still get multiple requests for a window
sequence number using the same periodUid. We should keep the initially
assigned number because no window change happened.

PiperOrigin-RevId: 268649009

library/core/src/main/java/com/google/android/exoplayer2/MediaPeriodQueue.java

@@ -454,7 +454,13 @@ import com.google.android.exoplayer2.util.Assertions;
       mediaPeriodHolder = mediaPeriodHolder.getNext();
       mediaPeriodHolder = mediaPeriodHolder.getNext();
     }
     }
     // If no match is found, create new sequence number.
     // If no match is found, create new sequence number.
-    return nextWindowSequenceNumber++;
+    long windowSequenceNumber = nextWindowSequenceNumber++;
+    if (playing == null) {
+      // If the queue is empty, save it as old front uid to allow later reuse.
+      oldFrontPeriodUid = periodUid;
+      oldFrontPeriodWindowSequenceNumber = windowSequenceNumber;
+    }
+    return windowSequenceNumber;
   }
   }
 
 
   /**
   /**