RimViewController::masterView() dereferenced ownerViewLinker() without a
null check, causing a crash when the controller has been detached from
its RimViewLinker parent (e.g. mid-destruction, after the owning
child-array field has already erased it but before delete runs).
The same unguarded ownerViewLinker() dereference existed in several other
methods: isActive(), isCameraLinked(), isTimeStepLinked(),
isResultColorControlled(), isLegendDefinitionsControlled(),
isPropertyFilterOveridden(), updateOverrides(),
updateDuplicatedPropertyFilters(), updateCameraLink(),
updateTimeStepLink(), updateResultColorsControl(),
updateLegendDefinitions() and applyCellFilterCollectionByUserChoice().
All now store ownerViewLinker() in a local and null-check it before use,
matching the pattern already used in isCellFiltersControlled().
