Add safeties to skip attempted import of the intro beatmap when osu! ruleset not present
Add safeties to skip attempted import of the intro beatmap when osu! ruleset not present

In general running this import will not cause any critical failures, but
the import itself *will* fail – and more loudly with the upcoming
changes to `RulesetStore` (https://github.com/ppy/osu/pull/16890). Due
to it being a loud failure, it will cause the notification overlay to
display a parsing error, which can interrupt the flow of some tests.

See test failure at
https://github.com/ppy/osu/runs/5268848949?check_suite_focus=true as an
example (video coverage at
https://github.com/ppy/osu/pull/16890#issuecomment-1046542243).

peppy/osu,peppy/osu,NeoAdonis/osu,NeoAdonis/osu,NeoAdonis/osu,ppy/osu,peppy/osu,ppy/osu,ppy/osu