Bug: `ClsCatch` in case expressions

[yoshihiro503]

The clauses in case expressions must be ClsCase, but not.

For example:

main(X) ->
    case X of
        {abc, Foo, Bar} -> ok
    end.

Current obeam (0.1.5) treats the clause in this code as an ClsCatch.

(ClsCatch (line 7) (line_cls 7) (line_stacktrace 7)
 (exception_class (AtomVarAtom (line 7) (atom abc)))
 (pattern (PatVar (line 7) (id Foo))) (stacktrace Bar) (guard_sequence ())
 (body (ExprBody (exprs ((ExprLit (lit (LitAtom (line 7) (atom ok)))))))))