ID 329903 - Live Rendering is not correctly sending light deletion updates

Problem summary:

When a light is disabled in the GafferThree node during a Live Render, an update is not sent to the render plug-in informing it of the location being deleted. This appears to only happen the first time a light is disabled, if it is enabled and disabled again, the delete update will be sent.

Steps to reproduce:

1. Open a Hello Pony scene.
2. Set /root to "include with children".
3. Start a Live Render.
4. Ensure the Live Render Monitor tab is open (from the dev resources repository https://phabricator.morefas.com/diffusion/DEV/).
5. In the GafferThree node, select the light, and press the 'D' key to disable it.
6. No update will be listed in the Live render Monitor tab.
7. Press the 'D' key twice more to toggle the light on and off again.
8. Updates would appear now (but not the first time!).

Expected behaviour:

An update should be displayed in the Live Render Monitor tab with an "attributes.deleted" attribute every time the light is deleted.

Actual behaviour:

The first time the light is deleted, no updates are sent at all.

Reproduced versions/platforms:

• 3.0v1a7