Fix port "0" listen

[Fangliding]

close #6636

[bytecategory]

我觉得不要急着合并, bye-panic这个分支代表了还有不少Build成功但"运行时具体状态"和下游假设不一致的问题.
例如
root@ubuntu:/fuzz# cat domain-udp-00114514.json
{
"inbounds": [
{
"listen": "",
"port": 11451,
"protocol": "dokodemo-door",
"settings": {
"udp": true
}
}
]
}
root@ubuntu:/fuzz# ./xray -c domain-udp-00114514.json
Xray 26.3.27 (Xray, Penetrates Everything.) d2758a0 (go1.26.1 linux/amd64)
A unified platform for anti-censorship.
2026/08/17 20:55:08.774167 [Info] infra/conf/serial: Reading config: &{Name:domain-udp-00114514.json Format:json}
panic: runtime error: index out of range [0] with length 0

goroutine 1 [running]:
github.com/xtls/xray-core/infra/conf.(*InboundDetourConfig).Build(0x1a883ddef948)
github.com/xtls/xray-core/infra/conf/xray.go:152 +0xeca
github.com/xtls/xray-core/infra/conf.(*Config).Build(0x1a883dcb32c0)
github.com/xtls/xray-core/infra/conf/xray.go:596 +0x188f
github.com/xtls/xray-core/infra/conf/serial.BuildConfig({0x1a883dc921c0?, 0x1a883dcbf050?, 0x1a883ddefbe8?})
github.com/xtls/xray-core/infra/conf/serial/builder.go:52 +0x2a
github.com/xtls/xray-core/core.LoadConfig({0x17d54c2, 0x4}, {0x15299e0?, 0x1a883dcbf050?})
github.com/xtls/xray-core/core/config.go:150 +0x56e
main.startXray()
github.com/xtls/xray-core/main/run.go:223 +0x15c
main.executeRun(0x26d20c0?, {0x1a883dc8b520?, 0x800883dc94700?, 0x7b56937201e8?})
github.com/xtls/xray-core/main/run.go:78 +0x130
github.com/xtls/xray-core/main/commands/base.Execute()
github.com/xtls/xray-core/main/commands/base/execute.go:64 +0x69f
main.main()
github.com/xtls/xray-core/main/main.go:22 +0x1a5