Simplify notification of downstream format change for embedded track

- There's no particular need to read or skip a sample before notifying
- Add missing isPendingReset check

Issue: #4533

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=211959762

library/core/src/main/java/com/google/android/exoplayer2/source/chunk/ChunkSampleStream.java

@@ -753,6 +753,10 @@ public class ChunkSampleStream<T extends ChunkSource> implements SampleStream, S
 
     @Override
     public int skipData(long positionUs) {
+      if (isPendingReset()) {
+        return 0;
+      }
+      maybeNotifyTrackFormatChanged();
       int skipCount;
       if (loadingFinished && positionUs > sampleQueue.getLargestQueuedTimestampUs()) {
         skipCount = sampleQueue.advanceToEnd();
@@ -762,9 +766,6 @@ public class ChunkSampleStream<T extends ChunkSource> implements SampleStream, S
           skipCount = 0;
         }
       }
-      if (skipCount > 0) {
-        maybeNotifyTrackFormatChanged();
-      }
       return skipCount;
     }
 
@@ -779,13 +780,9 @@ public class ChunkSampleStream<T extends ChunkSource> implements SampleStream, S
       if (isPendingReset()) {
         return C.RESULT_NOTHING_READ;
       }
-      int result =
-          sampleQueue.read(
-              formatHolder, buffer, formatRequired, loadingFinished, decodeOnlyUntilPositionUs);
-      if (result == C.RESULT_BUFFER_READ) {
-        maybeNotifyTrackFormatChanged();
-      }
-      return result;
+      maybeNotifyTrackFormatChanged();
+      return sampleQueue.read(
+          formatHolder, buffer, formatRequired, loadingFinished, decodeOnlyUntilPositionUs);
     }
 
     public void release() {