Fixes a runtime in spiders.dm attackby()

[Birdtalon]

About the pull request

[2023-12-03 16:02:14.678] runtime error: Cannot read null.len
 - proc name: attackby (/obj/effect/spider/attackby)
 -   source file: code/game/objects/effects/spiders.dm,24
 -   usr: Conner Scott (/mob/living/carbon/human)
 -   src: the spiderling (/obj/effect/spider/spiderling/nogrow)
 -   usr.loc: the floor (90,115,2) (/turf/open/floor/prison)
 -   src.loc: the catwalk (89,116,2) (/turf/open/floor/plating/plating_catwalk/prison)
 -   call stack:
 - the spiderling (/obj/effect/spider/spiderling/nogrow): attackby(the box of shotgun slugs (/obj/item/ammo_magazine/shotgun/slugs), Conner Scott (/mob/living/carbon/human), /list (/list))
 - Conner Scott (/mob/living/carbon/human): click adjacent(the spiderling (/obj/effect/spider/spiderling/nogrow), the box of shotgun slugs (/obj/item/ammo_magazine/shotgun/slugs), /list (/list))
 - Conner Scott (/mob/living/carbon/human): do click(the spiderling (/obj/effect/spider/spiderling/nogrow), the catwalk (89,116,2) (/turf/open/floor/plating/plating_catwalk/prison), "icon-x=18;icon-y=15;left=1;but...")
 - ****** (/client): Click(the spiderling (/obj/effect/spider/spiderling/nogrow), the catwalk (89,116,2) (/turf/open/floor/plating/plating_catwalk/prison), "mapwindow.map", "icon-x=18;icon-y=15;left=1;but...")

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Changelog

🆑
fix: Fixes runtime in spiders.dm
/🆑