 should not throw exception when calling SelectFields<T> with non-existing attributes.

repro:

```
cell MyCell {
[Attr1]
List<string> field;
}

var cell = Global.LocalStorage.NewGenericCell("MyCell", 0);
foreach(var f in cell.SelectFields<int>("Attr2")) {}
```

expect:
SelectFields enumerates nothing, but does not throw exception.

actual:
SelectFields throw an exception indicating data type <int> is not compatible with the cell.
