register session before loading plugin to be able to create callbacks in plugin

scheme/httpd/surflets/surflet-handler.scm

@@ -75,6 +75,7 @@
 				     (make-lock)          ; continuation table lock
 				     (make-thread-safe-counter))) ; continuation counter
 	  (release-lock *instance-table-lock*)
+	  (register-session! instance-id 'no-return)
 	  (let ((plugin (with-fatal-error-handler*
 			 (lambda (condition decline)
 			   (instance-delete! instance-id)
@@ -83,7 +84,6 @@
 			   (get-plugin-rt-structure path-string servlet-path)))))
 	    (reset
 	     (begin
-	       (register-session! instance-id 'no-return)
 	       (with-cwd
 		servlet-path
 		(with-names-from-rt-structure