Binary '.exe' is not defined
When using `nimble run` on Windows I get
```
Error: Binary '.exe' is not defined in 'mypackage' package.
```

How to reproduce:
* Use nimble init
* Choose Binary as project type
* Run `nimble build`
* Run `nimble run`

Nim version 1.0.2
Nimble version 0.11.0
(Both installed with choosenim -> stable)