Fix bg process api endpoint. return all users processes

src/api/endpoints/class-tainacan-rest-background-processes-controller.php

@@ -155,7 +155,7 @@ class REST_Background_Processes_Controller extends REST_Controller {
                 $user_q = $wpdb->prepare("AND user_id = %d", $request['user_id']);
             }
 
-            if ( isset($user_q['all_users']) && $user_q['all_users'] ) {
+            if ( isset($request['all_users']) && $request['all_users'] ) {
                 $user_q = "";
             }
         }