Deleting and reconstructing crossovers causes crash

[leemi]

1. Open Maya
2. Open Script Editor
3. Click CadNano
4. Click Honeycomb
5. Add 2 adjacent scaffold strands
6. Extend the strands all the way to the right
7. Add a crossover on the right (Creating a C with the right strands)
8. Delete the top left strand
9. Click on the crossover point on the top strand to break the crossover
10. Click again

// Warning: line 1: Nothing is selected. Select objects or components to delete. // 
# Traceback (most recent call last):
#   File "c:\git\cadnano2\views\pathview\pathselection.py", line 261, in itemChange
#     self.setParentItem(self.selectionbox.boxParent())
#   File "c:\git\cadnano2\views\pathview\pathselection.py", line 491, in boxParent
#     temp = self._itemGroup.childItems()[0].partItem()
#   File "c:\git\cadnano2\views\pathview\strand\stranditem.py", line 254, in partItem
#     return self._virtualHelixItem.partItem()
# AttributeError: 'NoneType' object has no attribute 'partItem'
# Traceback (most recent call last):
#   File "c:\git\cadnano2\views\pathview\pathselection.py", line 261, in itemChange
#     self.setParentItem(self.selectionbox.boxParent())
#   File "c:\git\cadnano2\views\pathview\pathselection.py", line 491, in boxParent
#     temp = self._itemGroup.childItems()[0].partItem()
#   File "c:\git\cadnano2\views\pathview\strand\endpointitem.py", line 130, in partItem
#     return self._strandItem.partItem()
#   File "c:\git\cadnano2\views\pathview\strand\stranditem.py", line 254, in partItem
#     return self._virtualHelixItem.partItem()
# AttributeError: 'NoneType' object has no attribute 'partItem'
# Traceback (most recent call last):
#   File "c:\git\cadnano2\views\pathview\strand\endpointitem.py", line 200, in mousePressEvent
#     getattr(self, toolMethodName)(modifiers, event, self.idx())  # call tool method
#   File "c:\git\cadnano2\views\pathview\strand\endpointitem.py", line 345, in selectToolMousePress
#     selectionGroup.processPendingToAddList()
#   File "c:\git\cadnano2\views\pathview\pathselection.py", line 123, in processPendingToAddList
#     item.modelSelect(doc)
#   File "c:\git\cadnano2\views\pathview\strand\endpointitem.py", line 488, in modelSelect
#     test = document.isModelStrandSelected(strand)
#   File "c:\git\cadnano2\model\document.py", line 147, in isModelStrandSelected
#     sS = strand.strandSet()
# AttributeError: 'NoneType' object has no attribute 'strandSet'
# Traceback (most recent call last):
#   File "c:\git\cadnano2\views\customqgraphicsview.py", line 406, in mouseReleaseEvent
#     self._selectionLock.processPendingToAddList()
#   File "c:\git\cadnano2\views\pathview\pathselection.py", line 123, in processPendingToAddList
#     item.modelSelect(doc)
#   File "c:\git\cadnano2\views\pathview\strand\endpointitem.py", line 488, in modelSelect
#     test = document.isModelStrandSelected(strand)
#   File "c:\git\cadnano2\model\document.py", line 147, in isModelStrandSelected
#     sS = strand.strandSet()
# AttributeError: 'NoneType' object has no attribute 'strandSet'

[grinner]

This was fixed with the documentClearSelectionsSignal, a selection and xover get installed simultaneously or something like that and we need to prevent the extra callback I think. This should be a separate issues.