RigStatisticsCalculator::mobileVolumeWeightedMean() accumulated into a sum
from an out-parameter that callees were not required to write. Every
implementation of the per time step overload has early-return paths that
leave the value untouched, as does RigWeightedMeanCalc::weightedMeanOverCells,
so indeterminate stack memory could be summed and presented in the UI.
Return std::optional<double> from the computation layer instead of using an
out-parameter, making "value not available" explicit and impossible to ignore:
- RigWeightedMeanCalc::weightedMeanOverCells
- RigStatisticsCalculator::mobileVolumeWeightedMean and all overrides
Time steps without a computable mean no longer contribute to the accumulated
sum, and are excluded from the divisor. Previously they would either add
garbage or, with a naive zero initialisation, bias the average towards zero.
RigStatisticsDataCache keeps the existing HUGE_VAL marker on its public API
via value_or(), so behaviour seen by RigHistogramData and the overlay info
is unchanged apart from the fix.
Also:
- Set m_isVolumeWeightedMeanCalculated in the per time step cache, which was
never assigned, so the cached value was recomputed on every call.
- Remove a duplicated ensureKnownResultLoaded() call in
RigEclipseNativeVisibleCellsStatCalc.
Fixes#14766