prevent 500 if add-on removed

apps/amo/views.py

@@ -69,7 +69,7 @@ def get_addon_details_from_amo(request, pk):
         revision.package.amo_slug = amo_slug
         revision.package.save()
 
-    if amo_meta['slug']:
+    if amo_slug:
         amo_meta['view_on_amo_url'] = revision.package.get_view_on_amo_url()
         amo_meta['edit_on_amo_url'] = revision.package.get_edit_on_amo_url()