Unimported completions don't work when completion session starts with `throw new`

**Version Used**:
VS 2026 18.1.1

**Steps to Reproduce**:
```cs
void M()
{
$$
}
```
Start typing `throw new UnreahableException` at `$$`

**Expected Behavior**:
When I get after `throw new` I get `UnreahableException` as unimported completion item

**Actual Behavior**:
When I get after `throw new` I don't get _any_ unimported completions. However, if I stop and invoke completion session after `throw new` manually, I get unimported completions (including `UnreachableException`):


Start by reproducing the supplied C# example in Visual Studio 18.1.1, comparing automatic completion after `throw new` with a manually invoked session. Trace the completion path for unimported items; done means `UnreachableException` and other applicable unimported completions appear automatically after `throw new`.

Written by the indexing model from the issue text.