Add (not technically necessary 0xFF guard for clarity).

Without this, the byte is cast as follows (in bits) if the top
byte is set:

10000010 -> 1000000000000000000000000000010

This works because we then always shift at least one bit left,
and only look at the bottom 8 bits of the result. It's confusing
though. It's clearer if the cast to int gives just adds zeros to
the front, like:

10000010 -> 0000000000000000000000010000010

library/src/main/java/com/google/android/exoplayer/util/BitArray.java

@@ -150,7 +150,7 @@ public final class BitArray {
   public int readUnsignedByte() {
     int value;
     if (bitOffset != 0) {
-      value = (data[byteOffset] << bitOffset)
+      value = ((data[byteOffset] & 0xFF) << bitOffset)
           | ((data[byteOffset + 1] & 0xFF) >>> (8 - bitOffset));
     } else {
       value = data[byteOffset];