Reset later item flag after defrag later is done (redis#12694)

Fixing issues described in redis#12672, started after redis#11695
Related to redis#12674

Fixes the `defrag didn't stop' issue.

In some cases of how the keys were stored in memory
defrag_later_item_in_progress was not getting reset once we finish
defragging the later items and we move to the next slot. This stopped
the scan to happen in the later slots and did not get 

Author: roshkhatri

src/defrag.c

@@ -1053,6 +1053,7 @@ void activeDefragCycle(void) {
                     continue;
                 }
                 slot = dbGetNextNonEmptySlot(db, slot, DB_MAIN);
+                defrag_later_item_in_progress = 0;
                 ctx.slot = slot;
             }