* 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.
