Fixed unintended dependency to porta_sale module

Portal Sale module was not thinke to use as a dependency but we
were calling an email template installed by that module causing
the send to customer action on ir_attachment_facturae to crash

l10n_mx_facturae/email_template.py

@@ -48,16 +48,21 @@ class email_template(orm.Model):
         )
         ir_model_data = self.pool.get('ir.model.data')
         # Look for possible templates for invoice and overrite
-        reference_ids.append(
-            ir_model_data.get_object_reference(
-                cr, uid, 'account', 'email_template_edi_invoice'
-            )[1]
-        )
-        reference_ids.append(
-            ir_model_data.get_object_reference(
-                cr, uid, 'portal_sale', 'email_template_edi_invoice'
-            )[1]
-        )
+        try:
+            reference_ids.append(
+                ir_model_data.get_object_reference(
+                    cr, uid, 'account', 'email_template_edi_invoice'
+                )[1]
+            )
+            reference_ids.append(
+                ir_model_data.get_object_reference(
+                    cr, uid, 'portal_sale', 'email_template_edi_invoice'
+                )[1]
+            )
+        except ValueError:
+            # Module porta_sale not installed so we catch the error
+            # and skip error messages
+            pass
         if template_id in reference_ids:
             att_obj = self.pool.get('ir.attachment.facturae.mx')
             states = ['printable', 'sent_customer', 'done']