Fix #705: Selection: reset range if start node was unrendered

When OnDemandList destroys far-off nodes, it can cause problems for
Selection and CellSelection if a long range selection is made after the
original start of the range was removed from the DOM.  This fix prevents
that case from throwing an error, though the range will still be reset.

CellSelection.js

@@ -83,10 +83,20 @@ return declare(Selection, {
 				this._selectionEventQueues[(value ? "" : "de") + "select"].push(cell);
 			}
 			if(toCell){
-				// a range
 				if(!toCell.element){
 					toCell = this.cell(toCell);
 				}
+
+				if(!toCell || !toCell.row){
+					this._lastSelected = element;
+					console.warn("The selection range has been reset because the " +
+						"beginning of the selection is no longer in the DOM. " +
+						"If you are using OnDemandList, you may wish to increase " +
+						"farOffRemoval to avoid this, but note that keeping more nodes " +
+						"in the DOM may impact performance.");
+					return;
+				}
+
 				var toElement = toCell.element;
 				var fromElement = cell.element;
 				// find if it is earlier or later in the DOM

Selection.js

@@ -500,6 +500,17 @@ return declare(null, {
 				if(!toRow.element){
 					toRow = this.row(toRow);
 				}
+
+				if(!toRow){
+					this._lastSelected = element;
+					console.warn("The selection range has been reset because the " +
+						"beginning of the selection is no longer in the DOM. " +
+						"If you are using OnDemandList, you may wish to increase " +
+						"farOffRemoval to avoid this, but note that keeping more nodes " +
+						"in the DOM may impact performance.");
+					return;
+				}
+
 				toElement = toRow.element;
 				// find if it is earlier or later in the DOM
 				traverser = (toElement && (toElement.compareDocumentPosition ?