Ticket #37531: 37531.4.diff

src/wp-admin/includes/ajax-actions.php

@@ -3601 +3601 @@
                 $status['debug'] = $upgrader->skin->get_upgrade_messages();
         }
 
+        if ( is_wp_error( $upgrader->skin->result ) ) {
+                $result = $upgrader->skin->result;
+        }
+
         if ( is_wp_error( $result ) ) {
                 $status['errorMessage'] = $result->get_error_message();
                 wp_send_json_error( $status );