Referencing export inside namespace doesn't add '____exports' prefix

```ts
export const foobar = "foobar";
namespace NS {
    if (foobar) {
        console.log("A");
    } else {
        console.log("B");
    }
}
```
=>
```lua
local ____exports = {}
____exports.foobar = "foobar"
local NS = {}
do
    if foobar then -- should be '____exports.foobar'
        print("A")
    else
        print("B")
    end
end
return ____exports
```
