fix(HLS): Avoid HLS resync when there is a gap in the stream (#5284)

lib/media/streaming_engine.js

@@ -640,10 +640,15 @@ shaka.media.StreamingEngine = class {
       const mediaState = this.mediaStates_.get(type);
       const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
 
-      // Always clear the iterator since we need to start streaming from the
-      // new time.  This also happens in clearBuffer_, but if we don't clear,
-      // we still want to reset the iterator.
-      mediaState.segmentIterator = null;
+      let segment = null;
+      if (mediaState.segmentIterator) {
+        segment = mediaState.segmentIterator.current();
+      }
+      // Only reset the iterator if we seek outside the current segment.
+      if (!segment || segment.startTime > presentationTime ||
+          segment.endTime < presentationTime) {
+        mediaState.segmentIterator = null;
+      }
 
       if (!newTimeIsBuffered(type)) {
         const bufferEnd =