fix: handle unhandled case in isCaptured (#1068)
fix: handle unhandled case in isCaptured (#1068)

Previously, this function missed a case, namely, one where the head of a
type definition contains a concrete struct, like `Maybe` with a variable
argument, `a`. That is,

```
(deftype (Foo (Maybe a)) [x (Maybe a)])
```

Would throw a type error. This commit fixes that issue.
eriksvedang/Carp,carp-lang/Carp,eriksvedang/Carp,carp-lang/Carp,carp-lang/Carp