Self referencing foreign key cannot be used with ``fk`` pragma
```nim
type
  Foo[T] {.tableName: "Fooz".} = ref object of Model
    name*: string
    desc*: string
    # fooid*: Option[Foo[T]] # <- This works
    fooid* {.fk: Foo.}: Option[int64] # <- This doesn't works
```

This is due to : 
* the condition evaluation around ``hasCustomPragma(fk)`` which expects an integer (so Option[int] is forbidden)
* A type referencing itself through the fk pragma is incoplete and is not seen as a Model during type evaluation. 