fix xmasked_view with xfunction

[gouarin]

Checklist

• The title and commit message(s) are descriptive.
• Small commits made to fix your PR have been squashed to avoid history pollution.
• Tests have been added for new features or bug fixes.
• API of new functions and classes are documented.

Description

[tdegeus]

@gouarin I'm not a big expert here so I cannot estimate what it takes to fix this. A question though: Should be aim to include this in the next release.

[gouarin]

I fixed the first issue but a new one appears. I had a discussion with @JohanMabille about that and it's not so easy to fix it.
We will take time together to find a solution after his vacation.