loader: do not output empty menu title

As we output spaces around the menu title, we should also check,
if the title is actually empty string.

PR:		255299
Submitted by:	Jose Luis Duran
Reported by:	Jose Luis Duran
MFC after:	1 week

stand/forth/menu.4th

@@ -490,7 +490,11 @@ also menu-infrastructure definitions
 		menuX @ 19 + over 2 / - menuY @ 1-
 	then
 	swap 1- swap
-	at-xy space type space
+	at-xy dup 0= if
+		2drop ( empty loader_menu_title )
+	else
+		space type space
+	then
 
 	\ If $menu_init is set, evaluate it (allowing for whole menus to be
 	\ constructed dynamically -- as this function could conceivably set

stand/lua/drawer.lua

@@ -286,9 +286,12 @@ local function drawbox()
 		menu_header_x = x + (w // 2) - (#menu_header // 2)
 	end
 	screen.setcursor(menu_header_x - 1, y)
+	if menu_header ~= "" then
 		printc(" " .. menu_header .. " ")
 	end
 
+end
+
 local function drawbrand()
 	local x = tonumber(loader.getenv("loader_brand_x")) or
 	    brand_position.x