Flicker/display corruption on external output unplug

When i unplug the external display i often get quite some flicker on the internal display even with !195 (merged) so there's either something odd in phoc, wlroots or mesa (maybe the kernel). A compositor restart fixes this. I'll work down the stack from here once i get a chance.

Nothing comparable is happening on intel with the same phoc but wlroots 0.11.0.