Fix unintitialized reference conflict on catch

An exception reference declared in a catch clause was considered as an unintitalised variable
when a closure parameter use the same name than the exception reference.

The following code works now as expected:

```golo
module InitializedReference

function main = |args| {
  let func = |e| {
    return e + 1
  }

 try {
   return func(41)
 } catch(e) {
    # may never happened
 }
}
```