Findlinks for specific subset of linklists deletes all objects stemming from other linklists

[PeterNerlich]

I don't know if there even is a way to know which object "belongs" to which linklist, but such a check would be very helpful for find_all_links() in utils.py. I discovered that just calling it with a subset of linklists did not produce the expected result.

Steps to reproduce

1. Ensure two linklists A and B exist drawing from distinct objects/fields
2. Ensure content exists for each of them containing links
3. Ensure populated db tables for linkcheck_link and linkcheck_url for objects of both linklists
4. Run find_all_links({"A": A})

Expected result

The function goes through each object covered by linklist A and creates new Url and Link objects where needed, and deletes old ones from linklist A that do not exist in content anymore. Objects involved with content from linklist B remain unchanged.

Actual result

The function goes through each object covered by linklist A and creates new Url and Link objects where needed, and deletes all objects not created or found, even if they belong to content for linklist B which is not being indexed. This leads to all objects from B being deleted.