api: do not fetch every patch in a patch detail view 404 (v2)

Commit 08c5856 fixed an issue whereby a 404 on the aforementioned URL
could result in a large DB query due to DRF attempting to populate the
'related' list box with all patches on the instance. That was
accidentally reverted in commit fe07f30. "Unrevert" this change.

Signed-off-by: Stephen Finucane <stephen@that.guru>
Fixes: fe07f30 ("Remove 'PatchRelationSerializer'")
Closes: #397
(cherry picked from commit 79700f3)

Author: stephenfin

patchwork/api/patch.py

@@ -84,7 +84,8 @@ class PatchListSerializer(BaseHyperlinkedModelSerializer):
     checks = SerializerMethodField()
     tags = SerializerMethodField()
     related = PatchSerializer(
-        source='related.patches', many=True, default=[])
+        source='related.patches', many=True, default=[],
+        style={'base_template': 'input.html'})
 
     def get_web_url(self, instance):
         request = self.context.get('request')