Remove the value-error for case when a boundary exists with an empty geometry

I ran Greece locally and I got the error: Boundary 1391 does not exist in the database. This is an empty existing boundary in the Boundaries table.

• Now, if we look in the exposureinitializer.py, in the line 219, there is a value error raise:

boundary_geometry = self.exposure_db.get_boundary_geometry(boundary_id)`
if boundary_geometry is None:
    raise ValueError(f"Boundary {boundary_id} does not exist in the database.")

• Looking into the exposure-lib, in the line 535 we have:

if result is not None:
    return result[0]
else:
    return None

So in case a boundary exists, but the geometry is empty,in the exposure-lib, the get inside the if statement. and then inside the exposure-initalizer, the boundary_geometry from the boundary_geometry = self.exposure_db.get_boundary_geometry(boundary_id) is a None! and the value error is then raised!

We should catch this case precisely or just print a warning instead.

@laurens @ds @shinde @gislars