Completing the final challenge at lower difficulties first doesn't give all points when solving at Expert

[auriamg]

From IRC:

bug is: I cannot get all 240 points in story mode
first I played all levels in silver, then in gold
but after defeating the castle villain, there where graphics glitches and I only could restart or leave the race
now all places on the map are golden, but the points are still 239 with one silver trophy
after restarting all is fine
let me check wether it happens again if I set fortmaga hard to false and win again
yep, same thing
there is no "you completed a challange"-animation
I can only restart or go back to challenge selection
where the fort becomes golden on the map
but the points are just 239

Migrated-From: https://sourceforge.net/apps/trac/supertuxkart/t/ticket/1140