fix: prevent panic when store.New returns nil session with error

Registry.Get panics with a nil pointer dereference when store.New
returns a nil session and a non-nil error. The code unconditionally
accesses session.name and session.store without checking for nil.

Add nil checks to prevent the panic and return the error instead.

Fixes #288

Author: Yanhu007

sessions.go

@@ -137,9 +137,14 @@ func (s *Registry) Get(store Store, name string) (session *Session, err error) {
 		session, err = info.s, info.e
 	} else {
 		session, err = store.New(s.request, name)
-		session.name = name
+		if session != nil {
+			session.name = name
+		}
 		s.sessions[name] = sessionInfo{s: session, e: err}
 	}
+	if session == nil {
+		return nil, err
+	}
 	session.store = store
 	return
 }