fix(errors) Fix a PHP error and hook error content

<p> cannot contain <pre> so we cannot use <pre> in hook error content.

issue #6071

include/errors/class_SimplePluginError.inc

@@ -48,7 +48,7 @@ class SimplePluginError extends FusionDirectoryError
       } elseif ($origin instanceof simpleTabs) {
         $this->tab    = NULL;
         $this->object = $origin;
-      } else {
+      } elseif ($origin !== NULL) {
         trigger_error('Invalid origin of class '.get_class($origin));
       }
     }

include/errors/class_SimplePluginHookError.inc

@@ -29,7 +29,7 @@ class SimplePluginHookError extends SimplePluginError
   {
     $this->hookType = $type;
 
-    parent::__construct($origin, '<pre><samp>'.htmlescape($output).'</samp></pre>', $code, $previous);
+    parent::__construct($origin, nl2br('<samp>'.htmlescape($output).'</samp>'), $code, $previous);
   }
 
   public function toArray (): array