Fix for v4: Admin returns "Too many pages" for subpages below top level (#6464)

* Fix for v4: Admin returns "Too many pages" for subpages below top level

Simple logic error during porting to new version it appears

* V4: LeftAndMain::getSiteTreeFor() returning space & New line in link

The "Too many pages" "View as list" link had a return &
  tab characters in it

* V4: LeftAndMain::getSiteTreeFor() fixes link for list view

"Too many pages" link pointed to `?view=list` which is
  just normal hierarchy. Value had been updated to "listview"
  in #8c87ea6b

admin/code/LeftAndMain.php

@@ -1188,7 +1188,7 @@ class LeftAndMain extends Controller implements PermissionProvider
             $nodeCountCallback = function ($parent, $numChildren) use (&$controller, $className, $nodeThresholdLeaf) {
                 if ($className !== 'SilverStripe\\CMS\\Model\\SiteTree'
                     || !$parent->ID
-                    || $numChildren >= $nodeThresholdLeaf
+                    || $numChildren <= $nodeThresholdLeaf
                 ) {
                     return null;
                 }
@@ -1199,8 +1199,7 @@ class LeftAndMain extends Controller implements PermissionProvider
                         _t('LeftAndMain.TooManyPages', 'Too many pages'),
                         Controller::join_links(
                             $controller->LinkWithSearch($controller->Link()),
-                            '
-							?view=list&ParentID=' . $parent->ID
+                            '?view=listview&ParentID=' . $parent->ID
                         ),
                         _t(
                             'LeftAndMain.ShowAsList',