backguard compatibility with mod default from older games

* this permits to use non player_api mod from default
* this permits to use older chest api by an aliase
* so this make to use this mod in 0.4 older deafult sub games

inventory.lua

@@ -84,6 +84,12 @@ mod.worn_items_inv = 'list[current_player;worn;0,3.5;2,4;]'
 mod.empty_button = 'image_button[2.25,2;1,1;transparent_button.png;dinv_empty_craft;Empty]'
 mod.fill_button = 'image_button[2.25,1;1,1;transparent_button.png;dinv_fill_craft;Fill]'
 
+-- backguard compatibility for older default mod, game pre 5.1 release 
+if not minetest.global_exists("default.chest") then
+	default.chest = {}
+	default.chest.get_chest_formspec = default.get_chest_formspec
+	minetest.log("warning", "[dinv] using older chest api from default mod")
+end
 
 -- All this is necessary to add scroll buttons to chests.
 if ADD_SCROLL_TO_DEFAULT_CHEST then
@@ -831,7 +837,11 @@ function mod.set_armor_textures(player)
 		end
 	end
 	textures = { tex }
-	player_api.set_textures(player, textures)
+	if minetest.get_modpath("player_api") then
+		player_api.set_textures(player, textures)
+	else
+		default.player_set_textures(player, textures)
+	end
 end