metrics: low space maybe wrong if tikv panic

[bufferflies]

Bug Report

What did you do?

What did you expect to see?

We should ignore the store if the capacity is 0B.

{
  "count": 4,
  "stores": [
    {
      "store": {
        "id": 4,
        "address": "db-tikv-0.db-tikv-peer.tidb1379661944632844070.svc:20160",
        "labels": [
          {
            "key": "host",
            "value": "ip-172-30-174-121.ap-northeast-1.compute.internal"
          },
          {
            "key": "region",
            "value": "ap-northeast-1"
          },
          {
            "key": "zone",
            "value": "ap-northeast-1d"
          }
        ],
        "version": "6.5.0",
        "peer_address": "db-tikv-0.db-tikv-peer.tidb1379661944632844070.svc:20160",
        "status_address": "db-tikv-0.db-tikv-peer.tidb1379661944632844070.svc:20180",
        "git_hash": "47b81680f75adc4b7200480cea5dbe46ae07c4b5",
        "start_timestamp": 1675135145,
        "deploy_path": "/",
        "last_heartbeat": 1679898149244798978,
        "state_name": "Offline"
      },
      "status": {
        "capacity": "0B",
        "available": "0B",
        "used_size": "0B",
        "leader_count": 0,
        "leader_weight": 1,
        "leader_score": 0,
        "leader_size": 0,
        "region_count": 3345,
        "region_weight": 1,
        "region_score": 264178,
        "region_size": 264178,
        "witness_count": 0,
        "slow_score": 0,
        "start_ts": "2023-01-31T03:19:05Z",
        "last_heartbeat_ts": "2023-03-27T06:22:29.244798978Z",
        "uptime": "1323h3m24.244798978s"
      }
    },
  ]
}

What did you see instead?

What version of PD are you using (pd-server -V)?

6.5.0

[HuSharp]

/assign

[bufferflies]

/assign @HuSharp