progress: Ensure missing start event is fired
The init function of the parent class fires a progress event for 0
progress rather than a start event. UI code was assuming that progress
events should always have a start event first. This change ensures that
the start event is correctly generated.
This fixes crashes that were seen in knotty in some configurations.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>