FIX: Move read state when moving posts

* Moves / copies post timings
* Moves / copies topic users
* Fixes a small bug in the calculation of post numbers

app/jobs/onceoff/clean_up_post_timings.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+module Jobs
+  class CleanUpPostTimings < Jobs::Onceoff
+
+    # Remove post timings that are remnants of previous post moves
+    # or other shenanigans and don't reference a valid user or post anymore.
+    def execute_onceoff(args)
+      DB.exec <<~SQL
+        DELETE
+        FROM post_timings pt
+        WHERE NOT EXISTS(
+                SELECT 1
+                FROM posts p
+                WHERE p.topic_id = pt.topic_id
+                  AND p.post_number = pt.post_number
+            )
+      SQL
+
+      DB.exec <<~SQL
+        DELETE
+        FROM post_timings pt
+        WHERE NOT EXISTS(
+                SELECT 1
+                FROM users u
+                WHERE pt.user_id = u.id
+            )
+      SQL
+    end
+  end
+end