crash in connectd due to bad gossip_store

[rustyrussell]

We hit an assert as we try to send a giant status message (> 128MB), but the reason we're sending it is because a gossip_store entry fails checksum. I accessed the gossip_store shortly after this, and it seemed fine.

The most likely explanation is that connectd somehow got a bogus offset, and was reading junk from the store.

lightning_connectd: FATAL SIGNAL (version v0.12.0)
0x414a56 send_backtrace
        common/daemon.c:33
0x41d10a status_failed
        common/status.c:221
0x41d1fc status_backtrace_exit
        common/subdaemon.c:18
0x414ada crashdump
        common/daemon.c:49
0x7f2a8063c31f ???
        ???:0
0x7f2a8063c2a2 ???
        ???:0
0x7f2a806258a3 ???
        ???:0
0x7f2a80625788 ???
        ???:0
0x7f2a80634a15 ???
        ???:0
0x42d90d wire_sync_write
        wire/wire_sync.c:13
0x414d75 daemon_conn_sync_flush
        common/daemon_conn.c:114
0x41cb31 flush_and_exit
        common/status.c:189
0x41d01a status_send_fatal
        common/status.c:206
0x41d102 status_failed
        common/status.c:223
0x416f16 gossip_store_next
        common/gossip_store.c:156
0x40d138 maybe_from_gossip_store
        connectd/multiplex.c:530
0x40d3fe write_to_peer
        connectd/multiplex.c:966
0x4aee10 next_plan
        ccan/ccan/io/io.c:59
0x4af210 io_do_always
        ccan/ccan/io/io.c:435
0x4aff02 handle_always
        ccan/ccan/io/poll.c:304
0x4b0229 io_loop
        ccan/ccan/io/poll.c:385
0x40b1db main
        connectd/connectd.c:2063
0x7f2a80626b74 ???
        ???:0
0x40481d ???
        ???:0
0xffffffffffffffff ???
        ???:0
lightning_connectd: wire/wire_sync.c:13: wire_sync_write: Assertion `tal_bytelen(msg) < WIRE_LEN_LIMIT' failed.
Lost connection to the RPC socket.Lost connection to the RPC socket.