MDL-51029 tool_lp: Before validate was not always called

When the validation already happened we did not call before_validate().
It must always be called as before_validate() can be used as if it was
a before_all() callback.

admin/tool/lp/classes/persistent.php

@@ -533,12 +533,12 @@ abstract class persistent {
     final public function validate() {
         global $CFG;
 
+        // Before validate hook.
+        $this->before_validate();
+
         // If this object has not been validated yet.
         if ($this->validated !== true) {
 
-            // Before validate hook.
-            $this->before_validate();
-
             $errors = array();
             $properties = static::properties_definition();
             foreach ($properties as $property => $definition) {