fix(p2p): guard conn.Close on dial error and close Exit_Event on shutdown

[moralpriest]

Summary

Two small reliability fixes in the P2P controller:

1. Nil-guard conn.Close() after failed KCP dial

   • connect_with_endpoint called conn.Close() unconditionally after kcp.DialWithOptions returned an error.
   • conn can be nil on error, causing a nil-pointer panic.
   • Added a nil check before closing.

2. Restore close(Exit_Event) in P2P_Shutdown

   • The shutdown signal channel was created but never closed (commented out).
   • Background goroutines (ping loop, chunk cleanup, sync engine, time check, ban cleanup) were left hanging until process death.
   • Uncommenting close(Exit_Event) allows them to exit cleanly.

Testing

• go build ./p2p/... and go test ./p2p/... pass.
• Manual: start derod, connect to peers, then exit — daemon shuts down without hanging.

Files changed

• p2p/controller.go

[8lecramm]

Merged commit 0f32a79.