Corrected undefined variable error in calendar.php

src/application/views/backend/calendar.php

@@ -122,6 +122,7 @@
                                         <?php
                                             // Group services by category, only if there is at least one service
                                             // with a parent category.
+                                            $has_category = FALSE;
                                             foreach($available_services as $service) {
                                                 if ($service['category_id'] != NULL) {
                                                     $has_category = TRUE;