fillna(0) workaround for artifacts without coordinates

[deppen8]

When importing artifacts from the database, 10 of them did not have corresponding survey points. This raises a couple of questions:

1. How did these artifacts get entered if there are no corresponding points? Were the points deleted accidentally?
2. What should we do about it?

For now, I have added a .fillna(0) to the Eastings and Northings in the leiap.spatial.find_geo_field() function. This allows the spatial join (gpd.sjoin()) to proceed without throwing an error, but it will cause headaches later if you try to map these artifacts, so it is not ideal behavior.

For the record, these are the artifacts:

• 160060-44-202-001
• 160060-44-202-002
• 160060-44-202-003
• 160060-44-203-001
• 160060-44-203-002
• 160060-44-204-001
• 160060-44-204-002
• 18038b-65-003-001
• 18038b-65-003-002
• 18038b-65-003-003