Small fixes for gpu-next and wayland

[cyanreg]

Something that doesn't really matter outside of my own experiment for gpu-next.

And a small fix for Wayland. It shouldn't be possible to have 2 presentation feedback events in-fly, so it should be safe to always zero it out.

[Dudemanguy]

Cherry-picked and pushed the second commit.

[sfan5]

@Dudemanguy can we just consistently get rid of dangling pointers in the wayland code?

[Dudemanguy]

The presentation stuff should have been the only ones.