seat: guard against button count corruption
seat: guard against button count corruption

This is still a compositor bug, and bad events will be sent to clients. We'll
need to track each button separately to handle this in wlroots.

ascent12/wlroots,swaywm/wlroots,swaywm/wlroots,ascent12/wlroots,SirCmpwn/wlroots