when we refresh the folder pane, clear the selection (workaround for bug in the tree widget)

mailnews/base/resources/content/widgetglue.js

@@ -414,6 +414,7 @@ function refreshFolderPane()
 {
     var folderTree = GetFolderTree();
     if (folderTree) {
+        tree.clearItemSelection();
         var root = folderTree.getAttribute('ref');
         folderTree.setAttribute('ref', root);
     }