Register Sale Line only when sale_price_list is activated

The extras_depend is on sale_price_list and not sale. If sale is activated but
not sale_price_list, the module may be loaded before sale and the Sale Line
would not yet be present in the Pool.

issue7391
review47381002

__init__.py

@@ -17,4 +17,4 @@ def register():
     Pool.register(
         sale.Line,
         module='product_price_list_dates', type_='model',
-        depends=['sale'])
+        depends=['sale_price_list'])