Handle AttributeErrors when reading file properties to database more gracefully

[tw4l]

Currently if there is an attribute error at any point during the parsing of a file's properties from a METS FSEntry into the AIPscan database, the file gets written to the database as an ISO disk image, which is likely to be misleading:

AIPscan/AIPscan/Aggregator/database_helpers.py

Lines 196 to 200 in a25d742

	except AttributeError:
	# File error/warning to log. Obviously this format may
	# be incorrect so it is our best guess.
	file_info["file_format"] = "ISO Disk Image File"
	file_info["puid"] = "fmt/468"

.

[ross-spencer]

There is a nod to this particular issue here: #47 (comment) as I hoped to leave space for the developer working on #47 to consider this. So connected to #47, but a valid assertion. I should also have been clearer that the root cause of this is in metsrw archivematica/Issues#1277

[tw4l]

Thanks @ross-spencer, I missed the connection to #47. That's good context!