Fix crashes reported by crash telemetry

* Use guarded pointer for delayed plot updates

The cached result definition can be deleted before the delayed update is
executed, causing a crash in the PVT and relative permeability plot panels.

* Guard against fracture definition without conductivity result

The list of conductivity result names is empty for some fracture
definitions, causing an out of range access when computing statistics.

* Guard against missing data source in custom VFP plot

The data source of a VFP table can be null, and the VFP tables are not
available until the data has been imported.

ApplicationLibCode/ReservoirDataModel/RigEnsembleFractureStatisticsCalculator.cpp

@@ -157,6 +157,7 @@ std::vector<double> RigEnsembleFractureStatisticsCalculator::calculateGridStatis
 {
     std::vector<double> samples;
     if ( fractureDefinitions.empty() ) return samples;
+    if ( fractureDefinitions[0]->conductivityResultNames().isEmpty() ) return samples;
 
     // TODO: heuristic to find conductivity name?
     QString conductivityResultName = fractureDefinitions[0]->conductivityResultNames()[0];
@@ -255,6 +256,7 @@ std::vector<double> RigEnsembleFractureStatisticsCalculator::calculateAreaWeight
 {
     std::vector<double> samples;
     if ( fractureDefinitions.empty() ) return samples;
+    if ( fractureDefinitions[0]->conductivityResultNames().isEmpty() ) return samples;
 
     // TODO: heuristic to find conductivity name?
     QString conductivityResultName = fractureDefinitions[0]->conductivityResultNames()[0];