Nil pointer in leveldb

[rjl493456442]

Hi, recently we received an issue report in Go-ethereum project, it's a leveldb relevant panic because of nil pointer.
The version we used is https://github.com/syndtr/goleveldb/blob/64b5b1c739545ed311fb9d9924d19d188fabdc83

The original stack trace can be found here.

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x31 pc=0x7359de]

goroutine 2322980 [running]:
github.com/syndtr/goleveldb/leveldb/table.(*Reader).newBlockIter(0xc0f97ffb60, 0x1, 0x0, 0x0, 0x0, 0x1, 0x0)
        github.com/syndtr/[email protected]/leveldb/table/reader.go:733 +0xbe
github.com/syndtr/goleveldb/leveldb/table.(*Reader).find(0xc0f97ffb60, 0xc0ff4e6240, 0x28, 0x28, 0x1, 0x0, 0xffffffffffffff00, 0x0, 0x0, 0x0, ...)
        github.com/syndtr/[email protected]/leveldb/table/reader.go:835 +0x1a5
github.com/syndtr/goleveldb/leveldb/table.(*Reader).Find(...)
        github.com/syndtr/[email protected]/leveldb/table/reader.go:922
github.com/syndtr/goleveldb/leveldb.(*tOps).find(0xc0001ef2c0, 0xc03df6a870, 0xc0ff4e6240, 0x28, 0x28, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
        github.com/syndtr/[email protected]/leveldb/table.go:450 +0x150
github.com/syndtr/goleveldb/leveldb.(*version).get.func1(0x5, 0xc03df6a870, 0x20)
        github.com/syndtr/[email protected]/leveldb/version.go:180 +0x465
github.com/syndtr/goleveldb/leveldb.(*version).walkOverlapping(0xc127a5cc60, 0x0, 0x0, 0x0, 0xc0ff4e6240, 0x28, 0x28, 0xc0e4e893b8, 0xc0e4e89388)
        github.com/syndtr/[email protected]/leveldb/version.go:128 +0x479
github.com/syndtr/goleveldb/leveldb.(*version).get(0xc127a5cc60, 0x0, 0x0, 0x0, 0xc0ff4e6240, 0x28, 0x28, 0x0, 0x19917b00, 0x0, ...)
        github.com/syndtr/[email protected]/leveldb/version.go:164 +0x2f1
github.com/syndtr/goleveldb/leveldb.(*DB).get(0xc0002bf180, 0x0, 0x0, 0x0, 0x0, 0xc0e16f2380, 0x20, 0x20, 0x540f9912, 0x0, ...)
        github.com/syndtr/[email protected]/leveldb/db.go:785 +0x385
github.com/syndtr/goleveldb/leveldb.(*DB).Get(0xc0002bf180, 0xc0e16f2380, 0x20, 0x20, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0)
        github.com/syndtr/[email protected]/leveldb/db.go:851 +0x13b
github.com/ethereum/go-ethereum/ethdb/leveldb.(*Database).Get(0xc000bbe800, 0xc0e16f2380, 0x20, 0x20, 0x10000c0ff4e6210, 0x7f521445d738, 0x0, 0x20, 0x7f523c3aa3c8)
        github.com/ethereum/go-ethereum/ethdb/leveldb/leveldb.go:189 +0x5a
github.com/ethereum/go-ethereum/core/rawdb.ReadTrieNode(...)
        github.com/ethereum/go-ethereum/core/rawdb/accessors_state.go:80
github.com/ethereum/go-ethereum/trie.(*Sync).children(0xc0e4bcffc0, 0xc008d88500, 0x17d8258, 0xc0271dba40, 0xb3, 0xb3, 0x17d8258, 0xc0271dba40, 0x0)
        github.com/ethereum/go-ethereum/trie/sync.go:424 +0x8f2
github.com/ethereum/go-ethereum/trie.(*Sync).Process(0xc0e4bcffc0, 0xd900a9b35239e6bc, 0xca98340f73c8bfa7, 0x957e224c68dc755b, 0xd23f87c51f7430cb, 0xc046e4a3c0, 0xb3, 0xb3, 0xc01230c138, 0x8)
        github.com/ethereum/go-ethereum/trie/sync.go:291 +0x245
github.com/ethereum/go-ethereum/eth/downloader.(*stateSync).processNodeData(0xc0d8fe6aa0, 0xc046e4a3c0, 0xb3, 0xb3, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0)
        github.com/ethereum/go-ethereum/eth/downloader/statesync.go:594 +0x19f
github.com/ethereum/go-ethereum/eth/downloader.(*stateSync).process(0xc0d8fe6aa0, 0xc10aa0e7e0, 0x0, 0x0, 0x0)
        github.com/ethereum/go-ethereum/eth/downloader/statesync.go:534 +0x170
github.com/ethereum/go-ethereum/eth/downloader.(*stateSync).loop(0xc0d8fe6aa0, 0x0, 0x0)
        github.com/ethereum/go-ethereum/eth/downloader/statesync.go:400 +0x527
github.com/ethereum/go-ethereum/eth/downloader.(*stateSync).run(0xc0d8fe6aa0)
        github.com/ethereum/go-ethereum/eth/downloader/statesync.go:320 +0xde
created by github.com/ethereum/go-ethereum/eth/downloader.(*Downloader).runStateSync
        github.com/ethereum/go-ethereum/eth/downloader/statesync.go:114 +0x1ef

Original issue link: ethereum/go-ethereum#23626