Init: possible confusion if base+modified schemas already exist but local project dir doesn't

Seen the following case:

• configuration file "base" and "modified" schemas already exist in the database
• the project directory does not exist yet

In this scenario, db-sync will download the MM project at a particular version, but it does not check project ID first. This is a potential problem, because db-sync may try to download a project that is incompatible with the data already stored in the database - this can result in trying to fetch project at e.g. version 1234, but project may not even exist in such version, so the project download will fail.

The fix should be to check project ID before project's download, and fail with error if they do not match.

Esamina il flusso di inizializzazione in cui db-sync scarica il progetto Mergin Maps e traccia il modo in cui gli schemi di base e modificati esistenti vengono letti dal database. Controlla l’ID del progetto prima del download; il lavoro è completato quando un ID incompatibile produce un errore invece di tentare il download.