[IMP] purchase: multiple improvements

1) Remove unnecessary comparison

If the minimum quantity required by the supplier is not met, the
supplier is not chosen. So it is not necessary to compare the quantity
of the supplier after the browse.

2) Ignore AccessError when adding to new supplier to product

This should not block the user to confirm the PO.

addons/purchase/purchase.py

@@ -8,7 +8,7 @@ from openerp.tools import DEFAULT_SERVER_DATETIME_FORMAT
 from openerp.tools.translate import _
 from openerp.tools.float_utils import float_is_zero, float_compare
 import openerp.addons.decimal_precision as dp
-from openerp.exceptions import UserError
+from openerp.exceptions import UserError, AccessError
 
 class PurchaseOrder(models.Model):
     _name = "purchase.order"
@@ -352,8 +352,10 @@ class PurchaseOrder(models.Model):
                 vals = {
                     'seller_ids': [(0, 0, supplierinfo)],
                 }
-                line.product_id.write(vals)
-
+                try:
+                    line.product_id.write(vals)
+                except AccessError:  # no write access rights -> just ignore
+                    break
 
 class PurchaseOrderLine(models.Model):
     _name = 'purchase.order.line'
@@ -587,11 +589,6 @@ class PurchaseOrderLine(models.Model):
             'quantity': quantity_seller_uom_id,
         })
 
-        # Switch quantity back in product_uom
-        quantity = max(quantity_seller_uom_id, product.seller_qty)
-        if quantity and seller_product_uom != product_uom:
-            quantity = seller_product_uom._compute_qty_obj(seller_product_uom, quantity, product_uom)
-
         price_unit = product.seller_price
         if price_unit and seller_currency_id != currency_id:
             price_unit = seller_currency_id.compute(price_unit, currency_id)