Make DefaultDashChunkSource more robust against empty segment timelines

Segment timelines are technically allowed to be empty, but not all places
add the necessary checks.

Issue: google/ExoPlayer#11014
PiperOrigin-RevId: 514722205
(cherry picked from commit 788132b)

libraries/exoplayer_dash/src/main/java/androidx/media3/exoplayer/dash/DefaultDashChunkSource.java

@@ -236,9 +236,12 @@ public long getAdjustedSeekPositionUs(long positionUs, SeekParameters seekParame
     // Segments are aligned across representations, so any segment index will do.
     for (RepresentationHolder representationHolder : representationHolders) {
       if (representationHolder.segmentIndex != null) {
+        long segmentCount = representationHolder.getSegmentCount();
+        if (segmentCount == 0) {
+          continue;
+        }
         long segmentNum = representationHolder.getSegmentNum(positionUs);
         long firstSyncUs = representationHolder.getSegmentStartTimeUs(segmentNum);
-        long segmentCount = representationHolder.getSegmentCount();
         long secondSyncUs =
             firstSyncUs < positionUs
                     && (segmentCount == DashSegmentIndex.INDEX_UNBOUNDED
@@ -594,7 +597,7 @@ private ArrayList<Representation> getRepresentations() {
   }
 
   private long getAvailableLiveDurationUs(long nowUnixTimeUs, long playbackPositionUs) {
-    if (!manifest.dynamic) {
+    if (!manifest.dynamic || representationHolders[0].getSegmentCount() == 0) {
       return C.TIME_UNSET;
     }
     long lastSegmentNum = representationHolders[0].getLastAvailableSegmentNum(nowUnixTimeUs);