Fix NaN issue for Learner1D R -> R^n

[Davide-sd]

Description

If a function evaluates over a point where it is not defined, NaN will be returned.
In the case of a function R -> R^n, it caused _update_scale to compute self._scale[1] = nan,
which in turns led to the evaluation of the function on all other points to be NaN, causing an
infinite loop, as reported in issue #339.

Using np.nanmin and np.nanmax in place of np.min and np.max seems to solve the issue.

Fixes #339

Checklist

• Fixed style issues using pre-commit run --all (first install using pip install pre-commit)
• pytest passed

Type of change

Check relevant option(s).

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• (Code) style fix or documentation update
• This change requires a documentation update

[basnijholt]

Thanks a lot for the fix @Davide-sd!

[basnijholt]

LGTM!

[Davide-sd]

Thanks @basnijholt .

I've run all tests twice on my local machine. In the first run everything appeared to be correct. On the second run the adaptive/tests/test_runner.py::test_ipyparallel_executor failed. Not sure why...