Not sure why these aren't being detected on master right now - they should be...
Also allows wheel events to pass through around them.
Closes #1763.
Closes #1757
We need to still perform selection if selectedBeatmap itself is null
Closes #1762
This avoids `SelectionChanged` potentially being invoked multiple times after `selectedBeatmapSet` is already `null`.
Not sure if we will keep this going forward (there will likely be an opaque tab control on the notifications overlay similar to options) but let's go with this for now.
Results in incorrect default formatting.