Fix error when searching for a namespace returned no results

pkg/models/namespace.go

@@ -487,6 +487,10 @@ func (n *Namespace) ReadAll(s *xorm.Session, a web.Auth, search string, page int
 
 	namespaceIDs, ownerIDs := getNamespaceOwnerIDs(namespaces)
 
+	if len(namespaceIDs) == 0 {
+		return nil, 0, 0, nil
+	}
+
 	subscriptionsMap, err := getNamespaceSubscriptions(s, namespaceIDs, doer.ID)
 	if err != nil {
 		return nil, 0, 0, err

pkg/models/namespace_test.go

@@ -346,4 +346,14 @@ func TestNamespace_ReadAll(t *testing.T) {
 		// Assert the first namespace is not the favorites namespace
 		assert.NotEqual(t, SavedFiltersPseudoNamespace.ID, namespaces[0].ID)
 	})
+	t.Run("no results", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		n := &Namespace{}
+		nn, _, _, err := n.ReadAll(s, user1, "some search string which will never return results", 1, -1)
+		assert.NoError(t, err)
+		assert.Nil(t, nn)
+	})
 }