Fix some ChromeVox Closure compiler errors.

chrome/browser/resources/chromeos/chromevox/walkers/table_walker.js

Index: chrome/browser/resources/chromeos/chromevox/walkers/table_walker.js
diff --git a/chrome/browser/resources/chromeos/chromevox/walkers/table_walker.js b/chrome/browser/resources/chromeos/chromevox/walkers/table_walker.js
index fa629cff824008a19c99c3eb2f45b44bcc9b8307..8e6a0e20ae8d6524ae318f09cce34d6a12071d74 100644
--- a/chrome/browser/resources/chromeos/chromevox/walkers/table_walker.js
+++ b/chrome/browser/resources/chromeos/chromevox/walkers/table_walker.js
@@ -384,6 +384,9 @@ cvox.TableWalker.prototype.isInTable = function(sel) {
  * @private
  */
 cvox.TableWalker.prototype.goTo_ = function(sel, f) {
+  if (!sel.end.node) {
+    return null;
+  }
   this.tt.initialize(this.getTableNode_(sel));
   var position = this.tt.findNearestCursor(sel.end.node);
   if (!position) {