Fix the preparation of Extractor inside the init() method

Extractor was not calling endTracks() and seekMap() on the
extractorOutput which are required to finish the preparation.
At that point extractor does not support seeking.

PiperOrigin-RevId: 393994848

library/extractor/src/main/java/com/google/android/exoplayer2/extractor/subtitle/SubtitleExtractor.java

@@ -27,6 +27,7 @@ import com.google.android.exoplayer2.extractor.Extractor;
 import com.google.android.exoplayer2.extractor.ExtractorInput;
 import com.google.android.exoplayer2.extractor.ExtractorOutput;
 import com.google.android.exoplayer2.extractor.PositionHolder;
+import com.google.android.exoplayer2.extractor.SeekMap;
 import com.google.android.exoplayer2.extractor.TrackOutput;
 import com.google.android.exoplayer2.text.Cue;
 import com.google.android.exoplayer2.text.CueEncoder;
@@ -117,6 +118,8 @@ public class SubtitleExtractor implements Extractor {
     checkState(state == STATE_CREATED);
     extractorOutput = output;
     trackOutput = extractorOutput.track(/* id= */ 0, C.TRACK_TYPE_TEXT);
+    extractorOutput.endTracks();
+    extractorOutput.seekMap(new SeekMap.Unseekable(C.TIME_UNSET));
     trackOutput.format(format);
     state = STATE_INITIALIZED;
   }