Fix raw parsing race condition
We get the initial dt_image_t from the database and then read the raw. The settings that come from the raw but not the database are not there. In the past we've papered over this by adding things to the db that have no business being there (e.g., raw_black and raw_maximum). Instead we can swap the correct dt_image_t into the pipeline at the same point we introduce the buffer itself into the pipe. Let the metadata flow together with the data.