Added a return code to load_maps

Added a return code to load_maps to check for if dynamic_add_media registers a fail.
Used by mcl_itemframes when reloading a map placed into an itemframe.

mods/ITEMS/mcl_maps/init.lua

@@ -22,6 +22,9 @@ local map_textures_path = worldpath .. "/mcl_maps/"
 
 minetest.mkdir(map_textures_path)
 
+-- overwrite the builtin tga_encoder
+dofile(modpath .. "/tga_encoder_init.lua")
+
 local function load_json_file(name)
     local file = assert(io.open(modpath .. "/" .. name .. ".json", "r"))
     local data = minetest.parse_json(file:read())
@@ -141,30 +144,43 @@ end
 
 function mcl_maps.load_map(id, callback)
     if id == "" or creating_maps[id] then
-		return
+        return false
     end
 
     local texture = "mcl_maps_map_texture_" .. id .. ".tga"
 
+    local result = true
+
     if not loaded_maps[id] then
         if not minetest.features.dynamic_add_media_table then
             -- minetest.dynamic_add_media() blocks in
             -- Minetest 5.3 and 5.4 until media loads
             loaded_maps[id] = true
-			dynamic_add_media(map_textures_path .. texture, function() end)
-			if callback then callback(texture) end
+            result = dynamic_add_media(map_textures_path .. texture, function()
+            end)
+            if callback then
+                callback(texture)
+            end
         else
             -- minetest.dynamic_add_media() never blocks
             -- in Minetest 5.5, callback runs after load
-			dynamic_add_media(map_textures_path .. texture, function()
+            result = dynamic_add_media(map_textures_path .. texture, function()
                 loaded_maps[id] = true
-				if callback then callback(texture) end
+                if callback then
+                    callback(texture)
+                end
             end)
         end
     end
 
+    if result == false then
+        return false
+    end
+
     if loaded_maps[id] then
-		if callback then callback(texture) end
+        if callback then
+            callback(texture)
+        end
         return texture
     end
 end