[FIX] tools: don't extract missing spreadsheet data source name

Previous versions of spreadsheet files don't have a name
for list and pivot datasources.

The spreadsheet template "pipeline dashboard" in `document_spreadsheet_crm`
is such a file.
As a consequence, exporting the source terms from this module fails
with a `KeyError: 'name'`

Part-of: odoo/odoo#101288