Fix bug with fire in Moontest

Moontest has no fire, yet CaveRealms references it.  Added conditionals.

nodes.lua

@@ -533,13 +533,17 @@ minetest.register_node("caverealms:constant_flame", {
 	damage_per_second = 4,
 	
 	after_place_node = function(pos, placer)
-		fire.on_flame_add_at(pos)
+		if pos.y > DM_TOP then
+			minetest.remove_node(pos)
+		end
+		if (minetest.get_modpath("moontest")) then
+			fire.on_flame_add_at(pos)
+		end
 	end,
 	
 	after_dig_node = function(pos, oldnode, oldmetadata, digger)
-		fire.on_flame_remove_at(pos)
-		if pos.y > DM_TOP then
-			minetest.remove_node(pos)
+		if (minetest.get_modpath("moontest")) then
+			fire.on_flame_remove_at(pos)
 		end
 	end,
 })