Make vendor field renderer show ID in readonly mode.

tailbone/forms/renderers/products.py

@@ -117,9 +117,14 @@ class VendorFieldRenderer(AutocompleteFieldRenderer):
     """
     Renderer for :class:`rattail.db.model.Vendor` instance fields.
     """
-
     service_route = 'vendors.autocomplete'
 
+    def render_readonly(self, **kwargs):
+        vendor = self.raw_value
+        if not vendor:
+            return ''
+        return "{0} - {1}".format(vendor.id, vendor.name)
+
 
 class PriceFieldRenderer(TextFieldRenderer):
     """