Fixed exception in RWStepShape_RWEdgeCurve::Check() thrown when trying
to access step entity in Interface_EntityIterator with zero entities.
Fixed a crash in StepToTopoDS_TranslateFace::Init() caused by
dereferencing nullptr.
RWStepShape_RWEdgeCurve and RWStepShape_RWEdgeCurve are refactored.
Test bug33665 is added to check the fixed behavior.