Warn if the working dir is exists but empty (on init)

[wonder-sk]

If the working dir has been created (but there's nothing in it), the init will fail when trying to get version of the mergin project. It would be useful to first do a check if there's a project there...

== Starting Mergin DB Sync version 1.0.6 ==
Logging in to Mergin...
Initializing from an existing GeoPackage...
Connecting to the database...
Traceback (most recent call last):
  File "dbsync.py", line 733, in <module>
    main()
  File "dbsync.py", line 714, in main
    dbsync_init(mc, True)
  File "dbsync.py", line 548, in dbsync_init
    local_version = _get_project_version()
  File "dbsync.py", line 242, in _get_project_version
    return mp.metadata["version"]
  File "/home/adriaan/.local/lib/python3.8/site-packages/mergin/merginproject.py", line 137, in metadata
    raise InvalidProject('Project metadata has not been created yet')
mergin.common.InvalidProject: Project metadata has not been created yet

[tomasMizera]

What is the expected behaviour here? Stop or automatically download the latest version?

[wonder-sk]

Fixed in #84 - if the working dir exists, but it is not a proper project dir (e.g. empty), it will be removed and reinitialized