Tweaks vent crawling.

The ability to ventcrawl is now checked by the /handle_ventcrawl() proc, making it possible to properly check before and after the do_after() call.
Moves various checks into the base can_ventcrawl proc.
Now lists the first object that prevents a mob from ventcrawling, making it easier to correct the exception list.
Removes the issmall() check, instead checks if the crawling mob has the relevant verb. Fixes #14081.

code/modules/ventcrawl/ventcrawl.dm

@@ -18,7 +18,15 @@ var/list/ventcrawl_machinery = list(
 /mob/var/next_play_vent = 0
 
 /mob/living/proc/can_ventcrawl()
-	return 0
+	if(!client)
+		return FALSE
+	if(!(/mob/living/proc/ventcrawl in verbs))
+		to_chat(src, "<span class='warning'>You don't possess the ability to ventcrawl!</span>")
+		return FALSE
+	if(incapacitated())
+		to_chat(src, "<span class='warning'>You cannot ventcrawl in your current state!</span>")
+		return FALSE
+	return ventcrawl_carry()
 
 /mob/living/Login()
 	. = ..()
@@ -29,9 +37,9 @@ var/list/ventcrawl_machinery = list(
 
 /mob/living/carbon/slime/can_ventcrawl()
 	if(Victim)
-		src << "<span class='warning'>You cannot ventcrawl while feeding.</span>"
-		return 0
-	return 1
+		to_chat(src, "<span class='warning'>You cannot ventcrawl while feeding.</span>")
+		return FALSE
+	. = ..()
 
 /mob/living/proc/is_allowed_vent_crawl_item(var/obj/item/carried_item)
 	if(carried_item == ability_master)
@@ -57,21 +65,18 @@ var/list/ventcrawl_machinery = list(
 	return ..()
 
 /mob/living/proc/ventcrawl_carry()
-	for(var/atom/A in src.contents)
+	for(var/atom/A in contents)
 		if(!is_allowed_vent_crawl_item(A))
-			src << "<span class='warning'>You can't be carrying that when vent crawling! - [A.name]</span>"
-			return 0
-	return 1
+			to_chat(src, "<span class='warning'>You can't carry \the [A] while ventcrawling!</span>")
+			return FALSE
+	return TRUE
 
 /mob/living/AltClickOn(var/atom/A)
-	if(is_type_in_list(A,ventcrawl_machinery) && src.can_ventcrawl())
-		src.handle_ventcrawl(A)
+	if(is_type_in_list(A,ventcrawl_machinery))
+		handle_ventcrawl(A)
 		return 1
 	return ..()
 
-/mob/living/carbon/human/can_ventcrawl()
-	return issmall(src)
-
 /mob/proc/start_ventcrawl()
 	var/atom/pipe
 	var/list/pipes = list()
@@ -88,36 +93,16 @@ var/list/ventcrawl_machinery = list(
 	if(canmove && pipe)
 		return pipe
 
-/mob/living/carbon/slime/can_ventcrawl()
-	return 1
-
-/mob/living/simple_animal/borer/can_ventcrawl()
-	return 1
-
-/mob/living/simple_animal/borer/ventcrawl_carry()
-	return 1
-
-/mob/living/simple_animal/mouse/can_ventcrawl()
-	return 1
-
-/mob/living/simple_animal/spiderbot/can_ventcrawl()
-	return 1
-
-/mob/living/carbon/alien/can_ventcrawl()
-	return 1
-
 /mob/living/carbon/alien/ventcrawl_carry()
 	return 1
 
 /mob/living/var/ventcrawl_layer = 3
 
 /mob/living/proc/handle_ventcrawl(var/atom/clicked_on)
-
-	if(!stat)
-		if(!lying)
+	if(!can_ventcrawl())
+		return
 
 	var/obj/machinery/atmospherics/unary/vent_found
-
 	if(clicked_on && Adjacent(clicked_on))
 		vent_found = clicked_on
 		if(!istype(vent_found) || !vent_found.can_crawl_through())
@@ -162,11 +147,7 @@ var/list/ventcrawl_machinery = list(
 
 			if(!do_after(src, 45, vent_found, 1, 1))
 				return
-
-					if(!client)
-						return
-
-					if(!ventcrawl_carry())
+			if(!can_ventcrawl())
 				return
 
 			visible_message("<B>[src] scrambles into the ventilation ducts!</B>", "You climb into the ventilation system.")
@@ -180,13 +161,6 @@ var/list/ventcrawl_machinery = list(
 	else
 		to_chat(src, "You must be standing on or beside an air vent to enter it.")
 
-		else
-			to_chat(src, "You can't vent crawl while you're stunned!")
-
-	else
-		to_chat(src, "You must be conscious to do this!")
-	return
-
 /mob/living/proc/add_ventcrawl(obj/machinery/atmospherics/starting_machine)
 	is_ventcrawling = 1
 	//candrop = 0

code/modules/ventcrawl/ventcrawl_verb.dm

@@ -2,8 +2,6 @@
 	set name = "Crawl through Vent"
 	set desc = "Enter an air vent and crawl through the pipe system."
 	set category = "Abilities"
-	if(incapacitated() || restrained())
-		return
 	var/pipe = start_ventcrawl()
 	if(pipe)
 		handle_ventcrawl()