Fix EventSampleStream's implementation regarding FLAG_REQUIRE_FORMAT

The current FLAG_REQUIRE_FORMAT documentation states: If an end of
stream buffer would be read were the flag not set, then behavior is
unchanged.

PiperOrigin-RevId: 380781976

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/EventSampleStream.java

@@ -100,18 +100,19 @@ import java.io.IOException;
   @Override
   public int readData(
       FormatHolder formatHolder, DecoderInputBuffer buffer, @ReadFlags int readFlags) {
+    boolean noMoreEventsInStream = currentIndex == eventTimesUs.length;
+    if (noMoreEventsInStream && !eventStreamAppendable) {
+      buffer.setFlags(C.BUFFER_FLAG_END_OF_STREAM);
+      return C.RESULT_BUFFER_READ;
+    }
     if ((readFlags & FLAG_REQUIRE_FORMAT) != 0 || !isFormatSentDownstream) {
       formatHolder.format = upstreamFormat;
       isFormatSentDownstream = true;
       return C.RESULT_FORMAT_READ;
     }
-    if (currentIndex == eventTimesUs.length) {
-      if (!eventStreamAppendable) {
-        buffer.setFlags(C.BUFFER_FLAG_END_OF_STREAM);
-        return C.RESULT_BUFFER_READ;
-      } else {
-        return C.RESULT_NOTHING_READ;
-      }
+    if (noMoreEventsInStream) {
+      // More events may be appended later.
+      return C.RESULT_NOTHING_READ;
     }
     int sampleIndex = currentIndex++;
     byte[] serializedEvent = eventMessageEncoder.encode(eventStream.events[sampleIndex]);

library/dash/src/test/java/com/google/android/exoplayer2/source/dash/EventSampleStreamTest.java

@@ -67,7 +67,10 @@ public final class EventSampleStreamTest {
   public void readDataReturnFormatForFirstRead() {
     EventStream eventStream =
         new EventStream(SCHEME_ID, VALUE, TIME_SCALE, new long[0], new EventMessage[0]);
-    EventSampleStream sampleStream = new EventSampleStream(eventStream, FORMAT, false);
+    // Make the event stream appendable so that the format is read. Otherwise, the format will be
+    // skipped and the end of input will be read.
+    EventSampleStream sampleStream =
+        new EventSampleStream(eventStream, FORMAT, /* eventStreamAppendable= */ true);
 
     int result = readData(sampleStream);
     assertThat(result).isEqualTo(C.RESULT_FORMAT_READ);