router(server): fix panic on server deletion

Fixes https://github.com/pterodactyl/panel/issues/5028

Signed-off-by: Matthew Penner <me@matthewp.io>

router/router_server.go

@@ -227,20 +227,19 @@ func deleteServer(c *gin.Context) {
 	//
 	// In addition, servers with large amounts of files can take some time to finish deleting,
 	// so we don't want to block the HTTP call while waiting on this.
-	go func(p string) {
-		_ = s.Filesystem().UnixFS().Close()
+	go func(s *server.Server) {
+		fs := s.Filesystem()
+		p := fs.Path()
+		_ = fs.UnixFS().Close()
 		if err := os.RemoveAll(p); err != nil {
 			log.WithFields(log.Fields{"path": p, "error": err}).Warn("failed to remove server files during deletion process")
 		}
-	}(s.Filesystem().Path())
+	}(s)
 
 	middleware.ExtractManager(c).Remove(func(server *server.Server) bool {
 		return server.ID() == s.ID()
 	})
 
-	// Deallocate the reference to this server.
-	s = nil
-
 	c.Status(http.StatusNoContent)
 }