Fixes Pushing Custodial Carts Slowing You Down (#15409)

code/modules/mob/mob.dm

@@ -1311,8 +1311,9 @@
 	if (dest != loc && istype(dest, /atom/movable))
 		AM = dest
 		LAZYADD(AM.contained_mobs, src)
-		if(pulledby)
-			pulledby.stop_pulling()
+		if(ismob(pulledby))
+			var/mob/M = pulledby
+			M.stop_pulling()
 
 	if (istype(loc, /atom/movable))
 		AM = loc

code/modules/mob/mob_movement.dm

@@ -339,7 +339,8 @@
 		//Wheelchair pushing goes here for now.
 		//TODO: Fuck wheelchairs.
 		if(istype(mob.pulledby, /obj/structure/bed/stool/chair/office/wheelchair) || istype(mob.pulledby, /obj/structure/janitorialcart))
-			move_delay += 1
+			var/obj/structure/S = mob.pulledby
+			move_delay += S.slowdown
 			return mob.pulledby.relaymove(mob, direct)
 
 		var/old_loc = mob.loc