Unexpected parsing behavior with semicolons

We have observed in #1074 that the parsed tree changes (modulo spans) depending on semicolons, which should not happen in these cases.

The cases giving different trees on `parseProgram`:

```scala
namespace list;
namespace internal;

val x = 4
val y = 5
```

vs.

```scala
namespace list
namespace internal

val x = 4
val y = 5
```

vs.

```scala
namespace list
namespace internal

val x = 4
val y = 5;
```

which can be reproduced by `(progA.defs zip progB.defs).foreach(assertEqualModuloSpans)`