The way this was handled previously is incorrect. We should still handle
creation of a capture session, just send `stopped` when it is created.
This can be tested by creating a capture source and session for a
workspace that has been removed. Toplevel and output sources have a
different issue in `smithay`: https://github.com/Smithay/smithay/pull/1961
Should fix https://github.com/pop-os/cosmic-epoch/issues/3319.
7fa5bd6b91