SIKFromAddress data race

[p4u]

Looks like there is a data race, probably the SIK tree is updated while, at the same time, a Get operation is performed.
When the tree is updated, the nodes on the tree change and those that are no longer required, are removed. If a Get operation is in course, it will fail at some point because some nodes of the Path do not exist anymore.

2023-11-22T14:00:34.636Z DBG middleware/logger.go:158 > "GET https://api-dev.vocdoni.net:443/metrics HTTP/2.0" from 95.217.216.185:54082 - 200 21252B in 14.135206ms
2023-11-22T14:00:43.088Z INF ipfs storage addresses=26934 peers=405 pins=2289
2023-11-22T14:00:43.81Z INF offchain downloader enqueued=0 retrying=0 total=447
2023-11-22T14:00:49.977Z INF vochain status blockTime="1m:10.00 10m:10.34 1h:10.40 6h:10.40 24h:10.40" elections=579 height=110053 mempool=0 peers=4 voteCache=0 votes=4883 votes/min=0
2023-11-22T14:00:50.702Z INF subpub network cluster=1 known=26957 peers=213
2023-11-22T14:00:51.371Z DBG ipfs/ipfs.go:314 > retrieved file /ipfs/bafybeigwsmihkf7krxkfuqejflfrao43g3ortsw4i6r6ouyzljp7mlci4e from cache
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x98 pc=0x2f38533]

goroutine 125009948 [running]:
github.com/cockroachdb/pebble.(*Batch).Get(0xc0175f2a48?, {0xc01d15ae10?, 0x0?, 0x0?})
	github.com/cockroachdb/[email protected]/batch.go:550 +0x13
go.vocdoni.io/dvote/db/pebbledb.get({0x4507ea0?, 0x0?}, {0xc01d15ae10?, 0x366d320?, 0x1?})
	go.vocdoni.io/dvote/db/pebbledb/pebledb.go:21 +0x33
go.vocdoni.io/dvote/db/pebbledb.(*WriteTx).Get(0x0?, {0xc01d15ae10?, 0x0?, 0x0?})
	go.vocdoni.io/dvote/db/pebbledb/pebledb.go:69 +0x2e
go.vocdoni.io/dvote/db/prefixeddb.(*PrefixedWriteTx).Get(0xc02635d4a0, {0xc00b77df12, 0x20, 0x0?})
	go.vocdoni.io/dvote/db/prefixeddb/prefixeddb.go:117 +0x10c
go.vocdoni.io/dvote/tree/arbo.(*Tree).down(0xc00f5358c0, {0x7f7f64cee2f8, 0xc02635d4a0}, {0xc015c6a330, 0x14, 0x14}, {0xc00b77df12, 0x20, 0x20}, {0xc016896c00, ...}, ...)
	go.vocdoni.io/dvote/tree/arbo/navigate.go:24 +0xee
go.vocdoni.io/dvote/tree/arbo.(*Tree).down(0xc00f5358c0, {0x7f7f64cee2f8, 0xc02635d4a0}, {0xc015c6a330, 0x14, 0x14}, {0xc00b77dea2, 0x20, 0x40}, {0xc016896c00, ...}, ...)
	go.vocdoni.io/dvote/tree/arbo/navigate.go:77 +0x851
go.vocdoni.io/dvote/tree/arbo.(*Tree).down(0xc00f5358c0, {0x7f7f64cee2f8, 0xc02635d4a0}, {0xc015c6a330, 0x14, 0x14}, {0xc00b77de72, 0x20, 0x20}, {0xc01f150ea0, ...}, ...)
	go.vocdoni.io/dvote/tree/arbo/navigate.go:82 +0xaaf
go.vocdoni.io/dvote/tree/arbo.(*Tree).down(0xc00f5358c0, {0x7f7f64cee2f8, 0xc02635d4a0}, {0xc015c6a330, 0x14, 0x14}, {0xc00b77ddd2, 0x20, 0x20}, {0xc01f150ea0, ...}, ...)
	go.vocdoni.io/dvote/tree/arbo/navigate.go:77 +0x851
go.vocdoni.io/dvote/tree/arbo.(*Tree).down(0xc00f5358c0, {0x7f7f64cee2f8, 0xc02635d4a0}, {0xc015c6a330, 0x14, 0x14}, {0xc00b77dd82, 0x20, 0x20}, {0xc00316c2a0, ...}, ...)
	go.vocdoni.io/dvote/tree/arbo/navigate.go:77 +0x851
go.vocdoni.io/dvote/tree/arbo.(*Tree).down(0xc00f5358c0, {0x7f7f64cee2f8, 0xc02635d4a0}, {0xc015c6a330, 0x14, 0x14}, {0xc00b77dd12, 0x20, 0x40}, {0xc02040d008, ...}, ...)
	go.vocdoni.io/dvote/tree/arbo/navigate.go:77 +0x851
go.vocdoni.io/dvote/tree/arbo.(*Tree).down(0xc00f5358c0, {0x7f7f64cee2f8, 0xc02635d4a0}, {0xc015c6a330, 0x14, 0x14}, {0xc016135f60, 0x20, 0x20}, {0x0, ...}, ...)
	go.vocdoni.io/dvote/tree/arbo/navigate.go:82 +0xaaf
go.vocdoni.io/dvote/tree/arbo.(*Tree).GetWithTx(0xc00f5358c0, {0x7f7f64cee2f8, 0xc02635d4a0}, {0xc015c6a330, 0x14, 0x14})
	go.vocdoni.io/dvote/tree/arbo/tree.go:541 +0x453
go.vocdoni.io/dvote/tree.(*Tree).Get(0x13c2e1d?, {0x7f7f64cee2f8?, 0xc02635d4a0?}, {0xc015c6a330?, 0x36cdd40?, 0x1c000230638?})
	go.vocdoni.io/dvote/tree/tree.go:70 +0x77
go.vocdoni.io/dvote/statedb.(*TreeUpdate).Get(...)
	go.vocdoni.io/dvote/statedb/treeupdate.go:63
go.vocdoni.io/dvote/statedb.(*TreeUpdate).DeepGet(0xc00316c000?, {0xc015c6a330, 0x14, 0x14}, {0xc00316c000?, 0x36cdd40?, 0xc00066a601?})
	go.vocdoni.io/dvote/statedb/treeupdate.go:192 +0x8f
go.vocdoni.io/dvote/statedb.(*treeUpdateView).DeepGet(0x3c94224?, {0xc015c6a330?, 0x0?, 0xab?}, {0xc00316c000?, 0xc016ed0a00?, 0xc0175f3d08?})
	go.vocdoni.io/dvote/statedb/treeupdate.go:378 +0x1d
go.vocdoni.io/dvote/vochain/state.(*State).SIKFromAddress(0x3631ac0?, {0x2e, 0x5b, 0x2, 0x23, 0x7f, 0x44, 0x89, 0xd5, 0x3a, ...})
	go.vocdoni.io/dvote/vochain/state/sik.go:46 +0x145
go.vocdoni.io/dvote/api.(*API).accountHandler(0xc00f7696c0, 0x25cd77b?, 0xc016bf0b60)
	go.vocdoni.io/dvote/api/accounts.go:150 +0x4b8
go.vocdoni.io/dvote/httprouter/apirest.(*API).RegisterMethod.func1({{0x35ed6e0, 0xc01644eb70}, {0xc14fa044d614e10a, 0x50020feb9464, 0x5fbd0a0}, {0xc00cffa390, 0x3, 0x3}, 0xc016bf0b60})
	go.vocdoni.io/dvote/httprouter/apirest/apirest.go:229 +0x6b
created by go.vocdoni.io/dvote/httprouter.(*HTTProuter).AddPublicHandler.(*HTTProuter).routerHandler.func1 in goroutine 125010181
	go.vocdoni.io/dvote/httprouter/httprouter.go:283 +0x3c5