[ast2] Empty object with anon struct
This C code:

```c
struct SDL_AudioCVT;

typedef struct SDL_AudioCVT
{
    int needed;
} SDL_AudioCVT;
```

Results in:

```nim
# Importing /Users/joey/Downloads/scratch/testover.h
# Generated at 2020-04-12T14:55:03-06:00
# Command line:
#   /Users/joey/.nimble/pkgs/nimterop-#cpluginpath/nimterop/toast --preprocess --pnim --nim:/Users/joey/Nim/bin/nim /Users/joey/Downloads/scratch/testover.h

{.hint[ConvFromXtoItselfNotNeeded]: off.}

import nimterop/types

{.pragma: imptestover, importc.}
{.pragma: imptestoverC, imptestover, cdecl.}

type
  SDL_AudioCVT* {.bycopy.} = object
```

But I would expect the output to be: 

```nim
# Importing /Users/joey/Downloads/scratch/testover.h
# Generated at 2020-04-12T14:52:56-06:00
# Command line:
#   /Users/joey/.nimble/pkgs/nimterop-#cpluginpath/nimterop/toast --preprocess --pnim --nim:/Users/joey/Nim/bin/nim /Users/joey/Downloads/scratch/testover.h

{.hint[ConvFromXtoItselfNotNeeded]: off.}

import nimterop/types

{.pragma: imptestover, importc.}
{.pragma: imptestoverC, imptestover, cdecl.}

type
  SDL_AudioCVT* {.bycopy.} = object
    needed*: cint
```