multi: fix `lnwallet.ErrDoubleSpend` #14780

Job	Run time
Sqlc check	2m 49s
lint code	7m 1s
check commits	6m 29s
cross compilation	13m 50s
RPC and mobile compilation check	4m 53s
sample configuration check	3m 41s
run macOS itest	43m 55s
run ubuntu itests (btcd, backend=btcd cover=1)	27m 16s
check pinned dependencies (google.golang.org/grpc v1.59.0)	6s
run ubuntu itests (bitcoind, backend=bitcoind cover=1)	32m 18s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	6s
run ubuntu itests (bitcoind-notxindex, backend="bitcoind notxindex")	31m 21s
run unit tests (btcd unit-cover)	16m 16s
run unit tests (unit tags="kvdb_etcd")	18m 19s
run ubuntu itests (bitcoind-rpcpolling, backend="bitcoind rpcpolling" cover=1)	31m 41s
run unit tests (unit tags="kvdb_postgres")	17m 19s
run ubuntu itests (bitcoind-etcd, backend=bitcoind dbbackend=etcd)	42m 25s
run windows itest	36m 17s
run unit tests (unit tags="kvdb_sqlite")	16m 9s
run ubuntu itests (bitcoind-postgres, backend=bitcoind dbbackend=postgres)	56m 50s
run unit tests (btcd unit-race)	34m 35s
run ubuntu itests (bitcoind-sqlite, backend=bitcoind dbbackend=sqlite)	33m 29s
run unit tests (unit-module)	3m 25s
run ubuntu itests (bitcoind-postgres-nativesql, backend=bitcoind dbbackend=postgres nativesql=true)	58m 2s
check release notes updated	5s
run ubuntu itests (bitcoind-sqlite-nativesql, backend=bitcoind dbbackend=sqlite nativesql=true)	32m 45s
run ubuntu itests (neutrino, backend=neutrino cover=1)	31m 26s
finish	6s
	10h 2m 54s

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