Revise dynamic_add_media API to better accomodate future changes

builtin/game/misc.lua

@@ -266,3 +266,26 @@ end
 function core.cancel_shutdown_requests()
 	core.request_shutdown("", false, -1)
 end
+
+
+-- Callback handling for dynamic_add_media
+
+local dynamic_add_media_raw = core.dynamic_add_media_raw
+core.dynamic_add_media_raw = nil
+function core.dynamic_add_media(filepath, callback)
+	local ret = dynamic_add_media_raw(filepath)
+	if ret == false then
+		return ret
+	end
+	if callback == nil then
+		core.log("deprecated", "Calling minetest.dynamic_add_media without "..
+			"a callback is deprecated and will stop working in future versions.")
+	else
+		-- At the moment async loading is not actually implemented, so we
+		-- immediately call the callback ourselves
+		for _, name in ipairs(ret) do
+			callback(name)
+		end
+	end
+	return true
+end