Fast switcher leaves windows translucent if they're removed while it's open

[kode54]

Describe the bug Windows which are hidden or removed from the toplevel view list between keypresses of Fast Switcher, while the modifier key is still held, stay translucent when they minimize themselves on switch. This affects, for instance, Minecraft.

To Reproduce Steps to reproduce the behavior:

1. Enable Fast Switcher
2. Launch a game of Minecraft
3. Fast Switch to another window
4. Minecraft is now stuck translucent until quit

Expected behavior Windows which have been removed from the list should have their alpha level restored.

Screenshots or stacktrace I may supply a screen shot of this.

Wayfire version 0.8.0, track-wlroots as well.

This may be difficult to fix, since the plugin just polls for the whole visible window list on every keypress, rather than maintaining a persistent copy of the list. It would need to diff the lists on update and fix any windows which have dropped out of the list, but haven't been destroyed yet.