fieldChangedByUi dereferenced m_geomCase->geoMechData() when changing the
reference time step or enabling hydrostatic pressure normalization. The data
is null when the case is not loaded. Use the null check already used
elsewhere in the file.
Crash stack (signature 4182d58e2359):
[3] RigGeoMechCaseData::femPartResults() at RigGeoMechCaseData.cpp:87
[4] RimGeoMechResultDefinition::fieldChangedByUi(...) at RimGeoMechResultDefinition.cpp:354