Amend HBASE-18026 ProtobufUtil seems to do extra array copying

If the ByteString is not a LiteralByteString, just do toByteArray().

Signed-off-by: Andrew Purtell <apurtell@apache.org>

hbase-protocol/src/main/java/com/google/protobuf/HBaseZeroCopyByteString.java

@@ -68,7 +68,7 @@ public final class HBaseZeroCopyByteString extends LiteralByteString {
     if (buf instanceof LiteralByteString) {
       return ((LiteralByteString) buf).bytes;
     }
-    throw new UnsupportedOperationException("Need a LiteralByteString, got a "
-                                            + buf.getClass().getName());
+    // In case it's BoundedByteString
+    return buf.toByteArray();
   }
 }