GHSA-5GQF-456P-4836 Reference binding to nullptr in `SdcaOptimizer`

Impact The implementation of tf.rawops.SdcaOptimizer triggers undefined behavior due to dereferencing a null pointer: python import tensorflow as tf sparseexampleindices = tf.constant0, dtype=tf.int64, tf.constant0, dtype=tf.int64 sparsefeatureindices = tf.constant, shape=0, 0, 0, 0,...