Fix data migration problems

[pombredanne]

See #812
@TG1999 can you further elaborate on this?

[TG1999]

Reference ID	URL
cpe:2.3:a:ibm:tklm:1.0:::::::*	https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:ibm:tklm:1.0:::::::*
--	--
cpe:2.3:a:ibm:tklm:1.0:::::::*	-

Previous data migration fix up cpe urls, but rerun of the importers somehow recreated CPEs with or without the URL and we ended up with duplicate cpe entries as before #785

[TG1999]

closed by #827

[pombredanne]

Based on a check the issue still exists:

{
    "reference_url": "",
    "reference_id": "cpe:2.3:a:lxml:lxml:*:*:*:*:*:*:*:*",
    "scores": [],
    "url": ""
},
{
    "reference_url": "https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:lxml:lxml:*:*:*:*:*:*:*:*",
    "reference_id": "cpe:2.3:a:lxml:lxml:*:*:*:*:*:*:*:*",
    "scores": [],
    "url": "https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:lxml:lxml:*:*:*:*:*:*:*:*"
},

[pombredanne]

I suggest two approaches:

1. a code review to ensure this is fixed for good
2. an improver to further fix this issue and similar issues

[TG1999]

Fixed in 6d379d0