Constraint buffered percentage to [0,100]

Issue: #2902

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=158142754

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java

@@ -305,10 +305,10 @@ import java.util.concurrent.CopyOnWriteArraySet;
     if (timeline.isEmpty()) {
       return 0;
     }
-    long bufferedPosition = getBufferedPosition();
+    long position = getBufferedPosition();
     long duration = getDuration();
-    return (bufferedPosition == C.TIME_UNSET || duration == C.TIME_UNSET) ? 0
-        : (int) (duration == 0 ? 100 : (bufferedPosition * 100) / duration);
+    return position == C.TIME_UNSET || duration == C.TIME_UNSET ? 0
+        : (duration == 0 ? 100 : Util.constrainValue((int) ((position * 100) / duration), 0, 100));
   }
 
   @Override