Fixes cooking machinery runtimes

Some recipes were sorted using paths that resulted in empty recipe types
(for example, /datum/recipe/microwave/human/burger causing an empty
/detum/recipe/microwave/human type to exist). These would be included in
the available recipes, and since their requirements are null, would all
be satisfied by anything in the machine. Since their result is null, a
runtime would occur while trying to create nothing.

This fixes some (all? Too lazy to test them all) kitchen machines never
failing.

code/modules/food/candy_maker.dm

@@ -33,7 +33,11 @@
 	if (!available_recipes)
 		available_recipes = new
 		for (var/type in (typesof(/datum/recipe/candy)-/datum/recipe/candy))
-			available_recipes+= new type
+			var/datum/recipe/recipe = new type
+			if(recipe.result) // Ignore recipe subtypes that lack a result
+				available_recipes += recipe
+			else
+				del(recipe)
 		acceptable_items = new
 		acceptable_reagents = new
 		for (var/datum/recipe/candy/recipe in available_recipes)

code/modules/food/grill_new.dm

@@ -34,7 +34,11 @@
 	if (!available_recipes)
 		available_recipes = new
 		for (var/type in (typesof(/datum/recipe/grill)-/datum/recipe/grill))
-			available_recipes+= new type
+			var/datum/recipe/recipe = new type
+			if(recipe.result) // Ignore recipe subtypes that lack a result
+				available_recipes += recipe
+			else
+				del(recipe)
 		acceptable_items = new
 		acceptable_reagents = new
 		for (var/datum/recipe/grill/recipe in available_recipes)

code/modules/food/oven_new.dm

@@ -34,7 +34,11 @@
 	if (!available_recipes)
 		available_recipes = new
 		for (var/type in (typesof(/datum/recipe/oven)-/datum/recipe/oven))
-			available_recipes+= new type
+			var/datum/recipe/recipe = new type
+			if(recipe.result) // Ignore recipe subtypes that lack a result
+				available_recipes += recipe
+			else
+				del(recipe)
 		acceptable_items = new
 		acceptable_reagents = new
 		for (var/datum/recipe/oven/recipe in available_recipes)