Fixing a crash in InsertListCommand.
There are two crash causes: 1.Range and 2.InsertListCommand.
In processAncestorsAndThierSiblings, it iterates siblings and remove each sibling.
Because removeChild might kick a “SubtreeModified” event which might change the tree structure,
ancestor might be not a parent of child at a next iteration. We should check it.
The doApply function does nothing when endingSelection().rootEditableElement() is Null.
Because L124 setEndingSelection might change endingSelection(), we should check again.