Fixes #7001 - Prints table headers when no data

Old behavior:
```$ hammer --output table repository list --organization org-7 --product product-without-repos```
```No data.```

New behavior:
```$ hammer --output table repository list --organization org-7 --product product-without-repos```
```
---|------|---------|--------------|----
ID | NAME | PRODUCT | CONTENT TYPE | URL
---|------|---------|--------------|----
```