fixed zero vote limit not respected and treated as unlimited (#224)

* fixed problem when zero vote limit was not respected and was treated as unlimited

* fixed TestRest_Vote

backend/app/rest/api/rest_test.go

@@ -98,6 +98,7 @@ func prep(t *testing.T) (srv *Rest, ts *httptest.Server) {
 		EditDuration:   5 * time.Minute,
 		MaxCommentSize: 4000,
 		AdminStore:     adminStore,
+		MaxVotes:       -1,
 	}
 	srv = &Rest{
 		DataService: dataStore,