fix(report): ignore exploits of no-cve-id vulns

[kotakanbe]

What did you implement:

In the current implementation, vuls report fills All exploits with no CVE-ID for the detected no-cve-id vulns. (The query is select * from exploits where cve_id = "")
This is a bug. So, don't fill exploits of no-cve-id vulns.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

./vuls report and then check the attack code is not included in the vulnerability without CVE-ID

Checklist:

• Write tests
• Write documentation
• Check that there aren't other open pull requests for the same issue/feature
• Format your source code by make fmt
• Pass the test by make test
• Provide verification config / commands
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES