Fix hasSampleFormat in experimental version. Oops!

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=115561885

library/src/main/java/com/google/android/exoplayer/chunk/InitializationChunk.java

@@ -78,7 +78,7 @@ public final class InitializationChunk extends Chunk implements SingleTrackOutpu
    * Should be called after loading has completed.
    */
   public boolean hasSampleFormat() {
-    return format != null;
+    return sampleFormat != null;
   }
 
   /**