backport some other getFlatIcon improvements so it compiles

code/__HELPERS/icons.dm

@@ -730,6 +730,10 @@ world
 				} \
 				current_layer = base_layer + appearance.layer + current_layer / 1000; \
 			} \
+			/* If we are using topdown rendering, chop that part off so things layer together as expected */ \
+			if((current_layer >= TOPDOWN_LAYER && current_layer < EFFECTS_LAYER) || current_layer > TOPDOWN_LAYER + EFFECTS_LAYER) { \
+				current_layer -= TOPDOWN_LAYER; \
+			} \
 			for (var/index_to_compare_to in 1 to layers.len) { \
 				var/compare_to = layers[index_to_compare_to]; \
 				if (current_layer < layers[compare_to]) { \
@@ -741,9 +745,10 @@ world
 		}
 
 	var/static/icon/flat_template = icon('icons/blanks/32x32.dmi', "nothing")
+	var/icon/flat = icon(flat_template)
 
 	if(!appearance || appearance.alpha <= 0)
-		return icon(flat_template)
+		return flat
 
 	if(start)
 		if(!defdir)
@@ -792,7 +797,6 @@ world
 	var/curblend = appearance.blend_mode || defblend
 
 	if(appearance.overlays.len || appearance.underlays.len)
-		var/icon/flat = icon(flat_template)
 		// Layers will be a sorted list of icons/overlays, based on the order in which they are displayed
 		var/list/layers = list()
 		var/image/copy