Error paths dereference an uninitialized pointer

The exact same pattern (const u8 *error; declared uninitialized, later conditionally set via sockpair(..., &error) before goto/fall-through to an error-send path) as in https://github.com/ElementsProject/lightning/issues/8849 also exists at

1. `lightningd/peer_control.c:1380 (connect_activate_subd())`
2. `lightningd/channel_control.c:331`

as reported by @Andezion