Fix storage close() null.vis_contents (#22521)

* Please describe the intent of your changes in a clear fashion.
This PR addresses a runtime error "Cannot modify null.vis_contents."
occurring in `/obj/item/storage/proc/close`.

**Problem:** The `close()` procedure for storage items was crashing when
attempting to modify `storage_start.vis_contents` because
`storage_start` was null.

**Root Cause:** The issue stemmed from stale `s_active` references on
mobs. When a storage item was destroyed, its `Destroy()` proc called
`close_all()`. However, `close_all()` (via `can_see_contents()`) only
cleared `s_active` for mobs with an active client. If a mob was
clientless (e.g., due to a brief disconnect) during the storage's
destruction, their `s_active` would retain a reference to the
now-destroyed storage. Later, if `Move()` was called on this mob (e.g.,
due to inertial drift), it would attempt to call `s_active.close(src)`
on the stale reference. Since the storage object was already destroyed
and `storage_start` had been `QDEL_NULL`ed, accessing
`storage_start.vis_contents` resulted in a null dereference.

**Solution:**
1. **Clear all stale `s_active` references in `Destroy()`:** Modified
`/obj/item/storage/Destroy()` to explicitly iterate through all mobs in
`is_seeing` after `close_all()` and nullify their `s_active` if it
points to the current storage object, regardless of their client status.
This ensures no stale references persist after the storage is destroyed.
2. **Add null guard for `storage_start` in `close()`:** Implemented a
defensive `if(storage_start)` check before accessing
`storage_start.vis_contents` in `/obj/item/storage/proc/close`. This
prevents a crash even if, under unforeseen circumstances,
`storage_start` is null when `close()` is invoked.

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images of these changes in the PR's description.
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comment with !wip or !review required
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yourself specify the license and original author below.
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changelog as specified in the contributor guidelines

### Asset Licenses
The following assets that **have not** been created by myself are
included in this PR:

| Path | Original Author | License |
| --- | --- | --- |
| icons/example.dmi | ExamplePerson (Example Station) | CC0 |


Fixes SERVER-PROD-TV

---------

Co-authored-by: sentry[bot] <39604003+sentry[bot]@users.noreply.github.com>
Co-authored-by: VMSolidus <evilexecutive@gmail.com>

code/game/objects/items/weapons/storage/storage.dm

@@ -93,6 +93,9 @@
 
 /obj/item/storage/Destroy()
 	close_all()
+	for(var/mob/M in is_seeing)
+		if(M.s_active == src)
+			M.s_active = null
 	QDEL_NULL(boxes)
 	QDEL_NULL(storage_start)
 	QDEL_NULL(storage_continue)
@@ -313,7 +316,8 @@
 	hide_from(user)
 	user.s_active = null
 	if(!length(can_see_contents()))
-		storage_start.vis_contents = list()
+		if(storage_start)
+			storage_start.vis_contents = list()
 		QDEL_LIST(storage_screens)
 		storage_screens = list()