Don't replace allowed quality unless from preferred quality

[fredhen]

• PR is based on the DEVELOP branch
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This is a proposed fix for #11710 by not downloading another Allowed quality if the existing download is already an Allowed quality in order to be in line with the Wiki https://github.com/pymedusa/Medusa/wiki/Quality-Settings#custom-qualities:

In short, if qualities are set in both the Allowed and Preferred categories, Medusa will download up to one release from the allowed category and one release from the preferred category even if a higher quality preferred release is released at a later date.