godef by expression not working with go/packages

I think this works without go/packages:
1. Create `hello.go`:
```go
package main

import "fmt"

func main() {
	fmt.Println("Hello, World!")
}
```
2. `go mod init`.
3. Run `godef -f hello.go fmt.Println`.
4. You get the error: `godef: Offset -1 was not a valid identifier`