core/state: fix typed nil panic in StopPrefetcher

commitAndFlush discarded errors from db.Reader() and db.Hasher() at
lines 1040-1041, storing the result directly into s.reader/s.hasher.
When Hasher() fails (e.g. newBinaryHasher returns nil, err), Go wraps
the nil *binaryHasher in the Hasher interface as a typed nil — an
interface value {type: *binaryHasher, value: nil} that passes == nil
checks. StopPrefetcher then type-asserts to Prefetcher (succeeds) and
calls TermPrefetch on the nil receiver, panicking at h.trie.term().

Fix: propagate errors from Reader() and Hasher() in commitAndFlush
instead of discarding them, and add defensive nil-receiver guards to
both binaryHasher.TermPrefetch and merkleHasher.TermPrefetch.

core/state/database_hasher_binary.go

@@ -387,5 +387,8 @@ func (h *binaryHasher) PrefetchStorage(addr common.Address, keys []common.Hash,
 
 // TermPrefetch terminates all prefetcher goroutines. Safe to call multiple times.
 func (h *binaryHasher) TermPrefetch() {
+	if h == nil {
+		return
+	}
 	h.trie.term()
 }

core/state/database_hasher_merkle.go

@@ -457,6 +457,9 @@ func (h *merkleHasher) PrefetchStorage(addr common.Address, keys []common.Hash,
 
 // TermPrefetch terminates all prefetcher goroutines. Safe to call multiple times.
 func (h *merkleHasher) TermPrefetch() {
+	if h == nil {
+		return
+	}
 	h.acctTrie.term()
 	for _, tr := range h.storageTries {
 		tr.term()

core/state/statedb.go

@@ -1040,8 +1040,18 @@ func (s *StateDB) commitAndFlush(block uint64, deleteEmptyObjects bool, noStorag
 	}
 	s.DatabaseCommits = time.Since(start)
 
-	s.reader, _ = s.db.Reader(s.originalRoot)
-	s.hasher, _ = s.db.Hasher(s.originalRoot)
+	reader, err := s.db.Reader(s.originalRoot)
+	if err != nil {
+		return nil, err
+	}
+	s.reader = reader
+
+	hasher, err := s.db.Hasher(s.originalRoot)
+	if err != nil {
+		return nil, err
+	}
+	s.hasher = hasher
+
 	return ret, nil
 }