fix (schedule): Various bug fixes.

src/modules/schedule/cog.py

@@ -489,7 +489,8 @@ class ScheduleCog(LionCog):
                         session = slot.sessions.get(guildid, None)
                         if session is None:
                             # Create a new session in the slot and set it up
-                            session = await slot.load_sessions(session_data[guildid, slotid])
+                            sessions = await slot.load_sessions([session_data[guildid, slotid]])
+                            session = sessions[guildid]
                             slot.sessions[guildid] = session
                             if slot.closing.is_set():
                                 # This should never happen

src/modules/schedule/core/timeslot.py

@@ -210,6 +210,7 @@ class TimeSlot:
             await batchrun_per_second(coros, 5)
 
             # Save messageids
+            if sessions:
                 tmptable = TemporaryTable(
                     '_gid', '_sid', '_mid',
                     types=('BIGINT', 'INTEGER', 'BIGINT')

src/utils/data.py

@@ -123,6 +123,9 @@ class TemporaryTable(Expression):
         AS
         name (col1, col2)
         """
+        if not self.values:
+            raise ValueError("Cannot flatten CTE with no values.")
+
         single_value = sql.SQL("({})").format(sql.SQL(", ").join(sql.Placeholder() for _ in self.columns))
         if self.types:
             first_value = sql.SQL("({})").format(