Handle collections without optional `item_assets` property

[anayeaye]

Description

Veda-docs example stac_ipyleaflet notebook is throwing exception
'message': 'Error caught with collection', 'error': KeyError('item_assets')

Surfaced in veda-docs PR NASA-IMPACT/veda-docs#160

I think
has_cog = True if data["item_assets"] else False
could be updated to something like has_cog = True if data.get("item_assets", None) else False

AC

• https://github.com/NASA-IMPACT/veda-docs/blob/main/notebooks/tutorials/stac_ipyleaflet.ipynb is runnable

[chuckwondo]

I think has_cog = True if data["item_assets"] else False could be updated to something like has_cog = True if data.get("item_assets", None) else False

Perhaps simply this? has_cog = "item_assets" in data