.this pragma doesn't work with generics

```nim
type
  A[T] = object
    x: T
{.this: self.}
proc testproc[T](self: A[T]) =
  echo x
```
```nim
type
  A = object
    x: int
{.this: self.}
proc testproc(self: A) =
  echo x
```
First example results in ` Error: undeclared identifier: 'x'`, second example compiles without issue.