CVE-2020-15199: Denial of Service in Tensorflow

The RaggedCountSparseOutput does not validate that the input arguments form a valid ragged tensor. In particular, there is no validation that the splits tensor has the minimum required number of elements. Code uses this quantity to initialize a different data structure: https://github.com/tensorflow/tensorflow/blob/0e68f4d3295eb0281a517c3662f6698992b7b2cf/tensorflow/core/kernels/count_ops.cc#L241-L244

Since BatchedMap is equivalent to a vector, it needs to have at least one element to not be nullptr. If user passes a splits tensor that is empty or has exactly one element, we get a SIGABRT signal raised by the operating system.