core/state: commit snapshot only if the base layer exists (#30493)

This pull request skips the state snapshot update if the base layer is
not existent, eliminating the numerous warning logs after an unclean
shutdown.

Specifically, Geth will rewind its chain head to a historical block
after unclean shutdown and state snapshot will be remained as unchanged
waiting for recovery. During this period of time, the snapshot is unusable
and all state updates should be ignored/skipped for state snapshot update.

core/state/statedb.go

@@ -1265,7 +1265,7 @@ func (s *StateDB) commitAndFlush(block uint64, deleteEmptyObjects bool) (*stateU
 	}
 	if !ret.empty() {
 		// If snapshotting is enabled, update the snapshot tree with this new version
-		if snap := s.db.Snapshot(); snap != nil {
+		if snap := s.db.Snapshot(); snap != nil && snap.Snapshot(ret.originRoot) != nil {
 			start := time.Now()
 			if err := snap.Update(ret.root, ret.originRoot, ret.destructs, ret.accounts, ret.storages); err != nil {
 				log.Warn("Failed to update snapshot tree", "from", ret.originRoot, "to", ret.root, "err", err)