[#189] sdk/netmap: Define unspecified clause

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/netmap/clause.go

@@ -9,7 +9,7 @@ import (
 type Clause uint32
 
 const (
-	_ Clause = iota
+	ClauseUnspecified Clause = iota
 
 	// ClauseSame is a selector modifier to select only nodes having the same value of bucket attribute.
 	ClauseSame
@@ -22,7 +22,7 @@ const (
 func ClauseFromV2(c netmap.Clause) Clause {
 	switch c {
 	default:
-		return 0
+		return ClauseUnspecified
 	case netmap.Same:
 		return ClauseSame
 	case netmap.Distinct:

pkg/netmap/clause_test.go

@@ -13,7 +13,7 @@ func TestClauseFromV2(t *testing.T) {
 		cV2 netmap.Clause
 	}{
 		{
-			c:   0,
+			c:   ClauseUnspecified,
 			cV2: netmap.UnspecifiedClause,
 		},
 		{