Point cloud dataset doesn't allow no-CRS data

[olsen232]

To Reproduce
kart import some-laz-file-that-doesnt-have-a-crs.laz
(You can agree to constrain-to-COPC or not - makes no difference.)

Expected behaviour
Should import the tiles, even with no CRS.

Output
A stacktrace, ending with:
RuntimeError: OGR Error: Corrupt data

Version Info
kart 0.14
affects all platforms

Also TODO: check if we support GeoTIFF files with no CRS

[craigds]

Should import the tiles, even with no CRS.

Not sure I agree, the LAS spec is fairly clear that a CRS header must be present. And it doesn't make much sense to just generate a fake/empty one:

https://www.asprs.org/wp-content/uploads/2019/03/LAS_1_4_r14.pdf

The Coordinate Reference System (CRS) information for the point data is required for all data.

IMO:

• we should have a --crs flag to kart point-cloud-import that lets you set/override the CRS of tiles while importing
• we should import tiles with no CRS into a dataset with a CRS, but set the CRS on the imported tiles to the same as the dataset
• we shouldn't let you import tiles with no CRS - i.e. if you're importing a new dataset from tiles that have no CRS, --crs will be required