grant doesn't find grant in grant image

**What happened**:

When scanning the grant docker image `anchore/grant:v0.6.4` using itself no packages and licenses are found

**What you expected to happen**:

then executable `/grant` is found and correctly identified as "Apache-2.0".

**Steps to reproduce the issue**:

```
docker run anchore/grant:v0.6.4 check image:anchore/grant:v0.6.4
✔ Loaded image:anchore/grant:v0.6.4 image
├── ✔ Packages [0 packages]
├── ✔ Licenses [0 unique]
└── ✔ File metadata [0 locations]
✔ Scanned for license compliance [0 packages]
```

**Anything else we need to know?**:

**Environment**:
- Output of `grant version`: 0.6.4
- OS (e.g: `cat /etc/os-release` or similar): docker

Start by reproducing the issue with `docker run anchore/grant:v0.6.4 check image:anchore/grant:v0.6.4` and inspect how the scanner handles the grant image. Done means the `/grant` executable is found and identified as Apache-2.0, with the package and license results no longer empty.

Written by the indexing model from the issue text.