Merge pull request #3400 from carlangas159/chamilo-lms-3222

Quiz: Exercise result: Exporting pdf is impossible - refs #3222

main/exercise/exercise_show.php

@@ -939,8 +939,7 @@ if ($show_results) {
 if ('export' === $action) {
     $content = ob_get_clean();
     // needed in order to mpdf to work
-    ob_clean();
-
+    if (ob_get_contents()) ob_clean();
     $params = [
         'filename' => api_replace_dangerous_char(
             $objExercise->name.' '.