Fix xdg-decoration unconfigured if set before first commit
Fix xdg-decoration unconfigured if set before first commit

In case a set_mode/unset_mode request is sent before the first commit, we need
to handle the value and send our preference accordingly.

This fixes xdg-decoration support for Qt apps.

SirCmpwn/sway,1ace/sway,ascent12/sway,ascent12/sway,ascent12/sway,1ace/sway,1ace/sway