Don't set room to null for expired images

Expiring them (also changed here to 0, rather that current time) is
enough to make them inaccessible now.

Author: jagerman

sogs/model/room.py

@@ -939,15 +939,14 @@ def delete_all_posts(self, poster: User, *, deleter: User):
             # TODO: Eventually we can drop this: once uploads have to be properly associated with
             # posts then the post deletion should trigger automatic expiry of post attachments.
 
-            # Don't actually delete right now but set room to NULL so that the images aren't
-            # retrievable, and set expiry to now so that they'll be picked up by the next db
-            # cleanup.
+            # Don't actually delete right now but just expire them so that the next db cleanup will
+            # perform the deletion (and since they are expired, they won't be accessible in the
+            # meantime).
             result = query(
                 f"""
-                UPDATE files SET room = NULL, expiry = :now WHERE room = :r AND uploader = :u
+                UPDATE files SET expiry = 0.0 WHERE room = :r AND uploader = :u
                     {'AND id != :omit' if omit_id else ''}
                 """,
-                now=time.time(),
                 r=self.id,
                 u=poster.id,
                 omit=omit_id,