Filter/Errors

* move checks to __construct so they can be run on $_POST data
   and don't create malformed filter urls
 * if we received malformed $_GET params, build new params and reload
 * do not store error state in cache
 * cleanup

includes/components/frontend/listview.class.php

@@ -146,9 +146,9 @@ class Listview implements \JsonSerializable
         $this->tabs = $tabVar;
     }
 
-    public function setError() : void
+    public function setError(bool $enable) : void
     {
-        $this->_errors = 1;
+        $this->_errors = $enable ? 1 : null;
     }
 
     public function jsonSerialize() : array