Give better diagnostics when trying to use kart rank and it's not set

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@5327 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/items/powerup.cpp

@@ -289,13 +289,12 @@ void Powerup::use()
  */
 void Powerup::hitBonusBox(int n, const Item &item, int add_info)
 {
-    unsigned int position = m_owner->getPosition();
-
+    int position = m_owner->getPosition();
+    assert(position != -1);
+    
     PowerupManager::PowerupType new_powerup = 
         powerup_manager->getRandomPowerup(position);
 
-    World *world = World::getWorld();
-
     if(m_type==PowerupManager::POWERUP_NOTHING)
     {
         set( new_powerup, n );

src/karts/kart.cpp

@@ -90,6 +90,7 @@ Kart::Kart (const std::string& ident, int position,
     m_saved_controller     = NULL;
 
     m_view_blocked_by_plunger = 0;
+    m_race_position           = -1;
 
     // Initialize custom sound vector (TODO: add back when properly done)
     // m_custom_sounds.resize(SFXManager::NUM_CUSTOMS);