output: reset the pending state on failed commit
output: reset the pending state on failed commit

It can be surprising for callers to stash pending changes, commit, get a
failure, then set some other pending changes, commit again, and get another
failure because of the previously-pending changes.

Instead, make commit reset the pending state on failure.

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