Fix clicking search link from song select sometimes not switching search mode to "relevance"

[peppy]

Noticed in normal usage. This is caused by the bound events happening in LoadComplete while the Search call from OsuGame.SearchBeatmapSet happens potentially before the first load of the overlay.

Also show the online search message even when there's no beatmaps loaded locally, which was a bit of an oversight.

[frenzibyte]

Was a bit confused on how it's not working given that there is a waitForReady method which doesn't execute the action until the overlay is loaded, but turns out it's the filter control which is not loaded, and can only be done when the overlay becomes visible for the first time. Makes sense.