Minor zetaclient nil pointer dereference

[renan061]

This is a "panic" error detected by chaos mode testing. It doesn't crash the node because the panic gets recovered.

Description In zetaclient/chains/bitcoin/observer/outbound.go:221 we can try to access a nil pointer p.

To Reproduce Run chaos mode with ZetacoreClient.GetPendingNonce failure rate set to 100.

2025-11-03T15:31:26Z ERR ../../../go/delivery/zeta-node/zetaclient/chains/bitcoin/observer/outbound.go:216 > error="error calling a zetacore client function (failed to get pending nonces): chaos error: ZetacoreClient.GetPendingNoncesByChain (0 < 5)" chain=18444 module=outbound network=btc
2025-11-03T15:31:26Z INF ../../../go/delivery/zeta-node/pkg/ticker/ticker.go:221 > Ticker stopped module=scheduler task_group=btc:18444 task_name=fetch_utxos task_type=interval_ticker ticker_name=fetch_utxos
2025-11-03T15:31:26Z ERR ../../../go/delivery/zeta-node/pkg/bg/bg.go:97 > Background task failed error="panic during ticker run: runtime error: invalid memory address or nil pointer dereference at /go/delivery/zeta-node/zetaclient/chains/bitcoin/observer/outbound.go:221 +0x98" module=scheduler task_group=btc:18444 task_name=fetch_utxos task_type=interval_ticker worker.name=unknown

Expected Behavior Function should return after logging the error in line 217.