state-surgery: safer memorydb (#3261)

Do not overwrite accounts that already exist when
creating accounts with the memory db. Also panic
if trying to set state in an account that doesn't
yet exist in the state.
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

state-surgery/state/memory_db.go

@@ -60,12 +60,15 @@ func (db *MemoryStateDB) CreateAccount(addr common.Address) {
 	db.rw.Lock()
 	defer db.rw.Unlock()
 
-	db.genesis.Alloc[addr] = core.GenesisAccount{
-		Code:    []byte{},
-		Storage: make(map[common.Hash]common.Hash),
-		Balance: big.NewInt(0),
-		Nonce:   0,
+	if _, ok := db.genesis.Alloc[addr]; !ok {
+		db.genesis.Alloc[addr] = core.GenesisAccount{
+			Code:    []byte{},
+			Storage: make(map[common.Hash]common.Hash),
+			Balance: big.NewInt(0),
+			Nonce:   0,
+		}
 	}
+
 }
 
 func (db *MemoryStateDB) SubBalance(addr common.Address, amount *big.Int) {
@@ -216,7 +219,7 @@ func (db *MemoryStateDB) SetState(addr common.Address, key, value common.Hash) {
 
 	account, ok := db.genesis.Alloc[addr]
 	if !ok {
-		return
+		panic(fmt.Sprintf("%s not in state", addr))
 	}
 	account.Storage[key] = value
 	db.genesis.Alloc[addr] = account