core: fix getOnPersistWrapper for native contracts

According to manifest, OnPersist.ReturnType is void, so we shouldn't
return anything from it. It's not so important, as we drop this value at
the end of OnPersist invocation.

pkg/core/native/native_nep5.go

@@ -2,6 +2,7 @@ package native
 
 import (
 	"errors"
+	"fmt"
 	"math/big"
 
 	"github.com/nspcc-dev/neo-go/pkg/core/dao"
@@ -303,6 +304,10 @@ func toUint160(s stackitem.Item) util.Uint160 {
 
 func getOnPersistWrapper(f func(ic *interop.Context) error) interop.Method {
 	return func(ic *interop.Context, _ []stackitem.Item) stackitem.Item {
-		return stackitem.NewBool(f(ic) == nil)
+		err := f(ic)
+		if err != nil {
+			panic(fmt.Errorf("OnPersist for native contract: %w", err))
+		}
+		return stackitem.Null{}
 	}
 }