Find releases past all-filtered-out pages on GitHub

[HebaruSan]

Problem

If a netkan has an asset_match that filters out the entire first page of releases on GitHub, then releases on later pages won't be found.

At the moment this only affects RP-0, which last had a matching release (starting with v1) six pages (19 months) ago:

• https://github.com/KSP-RO/RP-1/releases?page=6

(We might want to freeze that one anyway, if it's never going to have another release and is costing us 6 API hits per inflation...)

Cause

#4318 refactored the GitHub API to make a GithubRelease object accurately reflect the upstream data instead of processing it, which required moving the filtering logic from GithubRelease's constructor to GithubApi.GetAllReleases. In the process, the empty-page check was moved after the filtering instead of before, so the loop stopped at the first all-filtered-out page.

Changes

Now the empty-page check happens before the filtering.