Error message not displaying when select an incorrect flag size

When using the `pokemon` command with the `--image=xx` flag, if a non-valid size is used, no error will print, just a blank newline.

```shell
$ poke-cli pokemon umbreon --image=xl

# results in blank newline being printed instead of:
─────
Image
╭───────────────────────────╮
│Error!                     │
│Invalid image size.        │
│Valid sizes are: lg, md, sm│
╰───────────────────────────╯
```