System information

• Have I written custom code (as opposed to using a stock example script provided in TensorFlow): No
• OS Platform and Distribution (e.g., Linux Ubuntu 16.04): Linux Ubuntu 18.04
• Mobile device (e.g. iPhone 8, Pixel 2, Samsung Galaxy) if the issue happens on mobile device: N/A
• TensorFlow installed from (source or binary): binary
• TensorFlow version (use command below):2.1.0
• Python version:3.7.6
• Bazel version (if compiling from source):N/A
• GCC/Compiler version (if compiling from source):N/A
• CUDA/cuDNN version:N/A
• GPU model and memory:N/A

Describe the current behavior
tf.strings.substr crashes(aborts) when len(pos) > len(input)

Describe the expected behavior
expect an exception message if the input unexpected instead of crash.

Standalone code to reproduce the issue

import tensorflow as tf
tf.strings.substr(input='abc', len=1, pos=[1,-1])

import tensorflow as tf
tf.strings.substr(input='abc', len=1, pos=[1,2])

Output:

2021-02-03 22:46:41.234297: F ./tensorflow/core/framework/tensor.h:806] Check failed: new_num_elements == NumElements() (2 vs. 1)
Aborted (core dumped)