Outputs that are part of the layout but currently disabled (e.g. due
to use of wlr-output-power-management) are not correctly handled as
river currently waits for them to present a new locked frame before
sending the locked event.
This new frame never comes however since the output is disabled. Fix
this by maintaining the correct Output.lock_render_state as outputs
are enabled/disabled.
Additionally add missing maybeLock() calls to handle the case that all
outputs in the layout are disabled.
6c7586e8d7