fix: should return certificate correctly when there's no SNI provided in the request

[reaver-flomesh]

Bug description:

Affected area (please mark with X where applicable):

• Install [ ]
• Gateway API - GatewayClass [ ]
• Gateway API - Gateway [ ]
• Gateway API - HTTPRoute [ ]
• Gateway API - TLSRoute [ ]
• Gateway API - TCPRoute [ ]
• Gateway API - UDPRoute [ ]
• Gateway API - PolicyReference [ ]
• Ingress [x]
• Egress [ ]
• MultiCluster [ ]
• PIPY Control Plane [ ]
• PIPY Script/Config [ ]
• CLI Tool [ ]
• Metrics [ ]
• Certificate Management [x]
• Sidecar Injection [ ]
• Logging [ ]
• Debugging [ ]
• Tests [ ]
• Demo [ ]
• CI System [ ]

Expected behavior:

Steps to reproduce the bug (as precisely as possible):

How was FSM installed?:

Anything else we need to know?:

Bug report archive:

Environment:

• FSM version (use fsm version):
• Kubernetes version (use kubectl version):
• Size of cluster (number of worker nodes in the cluster):
• Others: