When overridden in a derived class, moves the System.Xml.XPath.XPathNavigator to the previous sibling node of the current node.
Returns true if the System.Xml.XPath.XPathNavigator is successful moving to the previous sibling node; otherwise, false if there is no previous sibling node or if the System.Xml.XPath.XPathNavigator is currently positioned on an attribute node. If false, the position of the System.Xml.XPath.XPathNavigator is unchanged.