Fix incorrect Javadoc

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=148633347

library/src/main/java/com/google/android/exoplayer2/extractor/mp4/Track.java

@@ -93,7 +93,7 @@ public final class Track {
   public final long[] editListMediaTimes;
   public final long[] editListMediaTimes;
 
 
   /**
   /**
-   * For H264 video tracks, the length in bytes of the NALUnitLength field in each sample. -1 for
+   * For H264 video tracks, the length in bytes of the NALUnitLength field in each sample. 0 for
    * other track types.
    * other track types.
    */
    */
   public final int nalUnitLengthFieldLength;
   public final int nalUnitLengthFieldLength;