FIX: Set undefined point attributes to masked instead of nan

[tnatt]

Yet another regression fix on #1117, this PR reverts back to masking undefined attribute values on roxar points instead of using nan values.

Was a bit tricky to detect, RMS accepts nan values when setting and getting roxar point attributes. However if an attribute contained any nan values an error occurred in the horizon modelling job, saying there were no data inside the model boundary for the specific horizon.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (77eb49b) 80.10% compared to head (5cc9192) 80.10%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1130 +/- ## ======================================= Coverage 80.10% 80.10% ======================================= Files 98 98 Lines 13609 13609 Branches 2197 2197 ======================================= Hits 10901 10901 Misses 1971 1971 Partials 737 737 ```

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