vendor: Update github.com/syndtr/goleveldb

vendor/github.com/syndtr/goleveldb/leveldb/db_state.go

@@ -7,6 +7,7 @@
 package leveldb
 
 import (
+	"errors"
 	"sync/atomic"
 	"time"
 
@@ -15,6 +16,10 @@ import (
 	"github.com/syndtr/goleveldb/leveldb/storage"
 )
 
+var (
+	errHasFrozenMem = errors.New("has frozen mem")
+)
+
 type memDB struct {
 	db *DB
 	*memdb.DB
@@ -126,7 +131,7 @@ func (db *DB) newMem(n int) (mem *memDB, err error) {
 	defer db.memMu.Unlock()
 
 	if db.frozenMem != nil {
-		panic("still has frozen mem")
+		return nil, errHasFrozenMem
 	}
 
 	if db.journal == nil {