Revert "timeline: Return FALSE when commiting an empty timeline"
This commit means that we do not get ASYNC_DONE anymore when commiting an empty timeline, which means that we need to special case that. This actually broke some code and does not bring in much. Fixes https://phabricator.freedesktop.org/T7802 Fixes https://phabricator.freedesktop.org/T7797 This reverts commit e570d1e0. Thanks @stefanzzz for investigating!