Initial commit of an XdgToplevel with a buffer already attached doesn't result in an error

[Supreeeme]

Observed on Niri. If a client commits the surface for an XdgToplevel with a buffer already attached, this should be a protocol error according to the XDG shell docs, but this does not appear to happen under Smithay. Instead, the compositor will appear to send the first configure using the size of the attached buffer. Does not happen under wlroots.t