Gnats 5442: SCT crash: right-clicking in empty area of series table
 with no cell selection.

Task: Check uses of the pointers returned from these SctDialog methods. 
(Pointers may be NULL). Also check direct uses of pointer fields.

 (a) SctSlotTstepSet* selSlotTstepSet()  const {return _selSlotTstepSet;}
 (b) SctSlotTstepSet* copySlotTstepSet() const {return _copySlotTstepSet;}
 (c) const SctSlotTstepSet* cachedRhSelection() 
        { return (_cachedRhSelSlotTstepSet); }

Changes in:
  void SctDialog::enaDispatching_Handler()
  void SctDialog::disDispatching_Handler()

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Gnats 544X:

This method may receive a NULL slotPtr! Crash when formatting message.

   bool SctModelData::checkSlotTstepSizeCompat (
                          QWidget* parent,    // can be NULL
                          DeltaTime sctStep,
                          Slot* slotPtr,
                          bool informUser,
                          bool& skipTstepSizeWarningsRet) const

   ...

   QString msg ("");
   msg.sprintf ("Slot \"%s\" has a %d %s timestep.\n"
            "Only series slots having a %d %s timestep\n"
            "are supported by this SCT.",
            qPrintable(slotPtr->getCompleteName()),
            (int) slotStep.time(), slotStep.unitsAsString(),
            (int) sctStep.time(), sctStep.unitsAsString());

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