[FIX] stock_account: no creating 2 def ir.property

property_stock_account_input_categ_id,
property_stock_account_output_categ_id,
property_stock_valuation_account_id ir.property default values on
product.category could be duplicated eg. if l10n_generic_coa was
installed before stock_account.

This did not happen in enterprise but happened in enterprise breaking
the test added in odoo/odoo@6bcf9ac2e.

addons/stock_account/data/stock_account_data_post_install.yml

@@ -56,7 +56,10 @@
                       'value': value,
                       'res_id': 'product.category,'+str(ref('product.product_category_all')),
                   }
-                  properties = PropertyObj.search([('name', '=', record), ('company_id', '=', company.id), ('value_reference', '!=', False)])
-                  if not properties:
-                      #create the property
+                  properties = PropertyObj.search([('name', '=', record), ('company_id', '=', company.id)])
+                  if properties:
+                      # the property exist: modify it
+                      properties.write(vals)
+                  else:
+                      # create the property
                       PropertyObj.create(vals)