fix: fix panic on Ledger derivation failure

[austinchandra]

Description

Closes: #XXX

Fix a panic (accessing array[0] of empty array) when either publicKey or address is not returned during Ledger derivation (e.g. when the Ethereum app is not open).

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[MalteHerrmann]

LGTM!

[fedekunze]

ACK, can you add a changelog entry?