refactor(audit-M2): drop nil-fallback workaround branch (consumes maps tile_at fix)

init.lua

@@ -29,14 +29,7 @@ function M.draw_map(map_id)
     local count = 0
     for ty = 0, size.h - 1 do
         for tx = 0, size.w - 1 do
-            -- maps.tile_at uses arity-dispatch: 2-arg form falls back to current map,
-            -- 3-arg form requires non-nil map_id. Branch to keep both call-shapes happy.
-            local t
-            if map_id == nil then
-                t = maps.tile_at(tx, ty)
-            else
-                t = maps.tile_at(map_id, tx, ty)
-            end
+            local t = maps.tile_at(map_id, tx, ty)
             if t ~= nil then
                 local c = tile_color(t)
                 local color = engine.render.rgb(c[1], c[2], c[3])