OverflowError in _disable_insert_blocking when using samples_per_insert=None

When using `samples_per_insert=None`, this [line](https://github.com/deepmind/acme/blob/26542510d8eff0cc05f31cc7dc66deee33040720/acme/jax/experiments/run_experiment.py#L277) returns the following error:
```
File "/home/kaleab/anaconda3/envs/dyn-net/lib/python3.9/site-packages/acme/jax/experiments/run_experiment.py", line 75, in run_experiment
replay_tables, rate_limiters_max_diff = _disable_insert_blocking(replay_tables)
File "/home/kaleab/anaconda3/envs/dyn-net/lib/python3.9/site-packages/acme/jax/experiments/run_experiment.py", line 296, in _disable_insert_blocking
max(1, int((rate_limiter_info.max_diff - rate_limiter_info.min_diff) / 2))
OverflowError: cannot convert float infinity to integer
```

,since `rate_limiter_info.max_diff` and `rate_limiter_info.min_diff` are inf, therefore `(rate_limiter_info.max_diff - rate_limiter_info.min_diff) / 2)` is inf as well.