Properly close disabled outputs restored during a restart. (#2337)

Properly close disabled outputs restored during a restart. (#2337)

If an output is disabled during a restart, for example because a binding
such as

    bindsym $mod+Shift+r exec "xrandr --auto", restart

is used, it can happen that we first write the layout to disk and only
then receive the RandR change events. This leads to a situation where
the restored tree will contain these outputs, but the restarted i3
process will not receive the RandR events, thus the internal output in i3
is marked disabled.

This patch finds these cases after a restart and force-disables the
affected outputs.

fixes #2326