Parent span does not contain child span (parser stability)

```scala
type i1 <: i1 = ; }
```
fails with
```
assertion failed: position error, parent span does not contain child span
parent      = case <error> => <error> # 7103499,
parent span = [17..18],
child       = <error> # 7103496,
child span  = <15..15>
```
AE-7b0a553f40029556f65e7ef447f3e51a94c6806a