Use int for an unsigned byte value in Cea608Decoder

This is a no-op, but it's more 'correct' because it avoids any potential
sign mix-ups that come from storing an unsigned byte (with a
potentially set MSB) in a signed java byte variable.

PiperOrigin-RevId: 483409798
(cherry picked from commit 3d0f43a1)

library/extractor/src/main/java/com/google/android/exoplayer2/text/cea/Cea608Decoder.java

@@ -458,8 +458,8 @@ public final class Cea608Decoder extends CeaDecoder {
     ccData.reset(subtitleData.array(), subtitleData.limit());
     ccData.reset(subtitleData.array(), subtitleData.limit());
     boolean captionDataProcessed = false;
     boolean captionDataProcessed = false;
     while (ccData.bytesLeft() >= packetLength) {
     while (ccData.bytesLeft() >= packetLength) {
-      byte ccHeader =
-          packetLength == 2 ? CC_IMPLICIT_DATA_HEADER : (byte) ccData.readUnsignedByte();
+      int ccHeader = packetLength == 2 ? CC_IMPLICIT_DATA_HEADER : ccData.readUnsignedByte();
+
       int ccByte1 = ccData.readUnsignedByte();
       int ccByte1 = ccData.readUnsignedByte();
       int ccByte2 = ccData.readUnsignedByte();
       int ccByte2 = ccData.readUnsignedByte();