[BUG] Unhandled Network Unreachable Error When No Gateway Defined

[pgwipeout]

The bug

While running Upsnap in an isolated container with no defined gateway (the management subnet is not permitted to jump to other subnets) the wake command would immediately terminate instead of counting down. The following is logged:
upsnap[94]: [ERROR] 2025/12/25 06:56:25 handlers.go:37: write udp [::]:54242->255.255.255.255:9: sendto: network is unreachable

This error is not observed with the wakeonlan program in the same container.

The OS that UpSnap is running on

Debian Trixie

Version of UpSnap

5.2.4

Your docker-compose.yml content

N/A

Reproduction steps

1. Create a container / vm with a static IP and no gateway defined or dynamic assigned address with a blank DHCP option `3`.
2. Run `upsnap serve --http=0.0.0.0:8090`.
3. Issue a wake command from Upsnap, observe the timer does not trigger.
4. Observe the error in the Upsnap terminal.

Additional information

Container is running in Proxmox 9 via the Proxmox VE Helper Scripts Repo, located at https://community-scripts.github.io/ProxmoxVE/scripts?id=upsnap&category=Network+%26+Firewall.