core: add InitializeCache method to NEO native contracts
There might be a case when cached contract values store nil (e.g.
after restoring chain from dump). We should always initialize cached
values irrespective to the (NEO).Initialize method.
This commit fixes a bug introduced in 83e94d3
when 4-nodes privnet is failing after restoring from dump:
```
$ docker logs neo_go_node_one
=> Try to restore blocks before running node
2020-09-30T11:55:49.122Z INFO no storage version found! creating genesis block
2020-09-30T11:55:49.124Z INFO service hasn't started since it's disabled {"service": "Pprof"}
2020-09-30T11:55:49.124Z INFO service hasn't started since it's disabled {"service": "Prometheus"}
2020-09-30T11:55:49.124Z INFO skipped genesis block {"hash": "3792eaa22c196399a114666fd491c4b9ac52491d9abb1f633a8036a8ac81e4db"}
2020-09-30T11:55:49.141Z INFO shutting down service {"service": "Pprof", "endpoint": ":30001"}
2020-09-30T11:55:49.141Z INFO shutting down service {"service": "Prometheus", "endpoint": ":40001"}
2020-09-30T11:55:49.141Z INFO blockchain persist completed {"persistedBlocks": 3, "persistedKeys": 146, "headerHeight": 3, "blockHeight": 3, "took": "324.27µs"}
2020-09-30T11:55:49.150Z INFO restoring blockchain {"version": "0.1.0"}
2020-09-30T11:55:49.150Z INFO service hasn't started since it's disabled {"service": "Prometheus"}
2020-09-30T11:55:49.151Z INFO service hasn't started since it's disabled {"service": "Pprof"}
2020-09-30T11:55:49.443Z INFO starting rpc-server {"endpoint": ":30333"}
2020-09-30T11:55:49.443Z INFO node started {"blockHeight": 3, "headerHeight": 3}
_ ____________ __________
/ | / / ____/ __ \ / ____/ __ \
/ |/ / __/ / / / /_____/ / __/ / / /
/ /| / /___/ /_/ /_____/ /_/ / /_/ /
/_/ |_/_____/\____/ \____/\____/
/NEO-GO:/
2020-09-30T11:55:49.444Z INFO new peer connected {"addr": "172.23.0.5:39638", "peerCount": 1}
2020-09-30T11:55:49.444Z INFO new peer connected {"addr": "172.23.0.5:20333", "peerCount": 2}
2020-09-30T11:55:49.444Z WARN peer disconnected {"addr": "172.23.0.5:20333", "reason": "identical node id", "peerCount": 1}
2020-09-30T11:55:49.445Z WARN peer disconnected {"addr": "172.23.0.5:39638", "reason": "identical node id", "peerCount": 0}
2020-09-30T11:55:49.445Z INFO new peer connected {"addr": "172.23.0.3:20335", "peerCount": 1}
2020-09-30T11:55:49.445Z INFO new peer connected {"addr": "172.23.0.2:20334", "peerCount": 2}
2020-09-30T11:55:49.445Z INFO started protocol {"addr": "172.23.0.3:20335", "userAgent": "/NEO-GO:/", "startHeight": 3, "id": 1339919829}
2020-09-30T11:55:49.445Z INFO new peer connected {"addr": "172.23.0.4:20336", "peerCount": 3}
2020-09-30T11:55:49.445Z INFO started protocol {"addr": "172.23.0.4:20336", "userAgent": "/NEO-GO:/", "startHeight": 3, "id": 4036722359}
2020-09-30T11:55:49.445Z INFO node reached synchronized state, starting consensus
2020-09-30T11:55:49.445Z INFO started protocol {"addr": "172.23.0.2:20334", "userAgent": "/NEO-GO:/", "startHeight": 3, "id": 1557367037}
panic: runtime error: integer divide by zero
goroutine 132 [running]:
github.com/nspcc-dev/dbft.(*Context).GetPrimaryIndex(...)
github.com/nspcc-dev/dbft@v0.0.0-20200925163137-8f3b9ab3b720/context.go:83
github.com/nspcc-dev/dbft.(*Context).reset(0xc0000e0780, 0x0)
github.com/nspcc-dev/dbft@v0.0.0-20200925163137-8f3b9ab3b720/context.go:208 +0x64b
github.com/nspcc-dev/dbft.(*DBFT).InitializeConsensus(0xc0000e0780, 0x964800)
github.com/nspcc-dev/dbft@v0.0.0-20200925163137-8f3b9ab3b720/dbft.go:87 +0x51
github.com/nspcc-dev/dbft.(*DBFT).Start(0xc0000e0780)
github.com/nspcc-dev/dbft@v0.0.0-20200925163137-8f3b9ab3b720/dbft.go:81 +0x4b
github.com/nspcc-dev/neo-go/pkg/consensus.(*service).Start(0xc0001a2160)
github.com/nspcc-dev/neo-go/pkg/consensus/consensus.go:206 +0x56
github.com/nspcc-dev/neo-go/pkg/network.(*Server).tryStartConsensus(0xc0000ec500)
github.com/nspcc-dev/neo-go/pkg/network/server.go:311 +0xda
github.com/nspcc-dev/neo-go/pkg/network.(*Server).handleMessage(0xc0000ec500, 0x104d800, 0xc000222090, 0xc0000a6f10, 0x0, 0x0)
github.com/nspcc-dev/neo-go/pkg/network/server.go:781 +0xa7a
github.com/nspcc-dev/neo-go/pkg/network.(*TCPPeer).handleConn(0xc000222090)
github.com/nspcc-dev/neo-go/pkg/network/tcp_peer.go:162 +0x2e7
created by github.com/nspcc-dev/neo-go/pkg/network.(*TCPTransport).Dial
github.com/nspcc-dev/neo-go/pkg/network/tcp_transport.go:40 +0x1ac
```
eccf639803