Fix compiler warning

src/items/powerup_manager.cpp

@@ -394,7 +394,7 @@ int PowerupManager::WeightsData::getRandomItem(int rank, unsigned int random_num
     if(rank>(int)m_summed_weights_for_rank.size())
         rank = m_summed_weights_for_rank.size()-1;
     else if (rank<0) rank = 0;  // E.g. battle mode, which has rank -1
-    const std::vector<int> &summed_weights = m_summed_weights_for_rank[rank];
+    const std::vector<unsigned> &summed_weights = m_summed_weights_for_rank[rank];
     // The last entry is the sum of all previous entries, i.e. the maximum
     // value
 #undef ITEM_DISTRIBUTION_DEBUG

src/items/powerup_manager.hpp

@@ -94,7 +94,7 @@ private:
         /** This field is only populated for the WeightData class that
          *  is used during a race. It contains for each rank the summed
          *  weights for easy lookup during a race. */
-        std::vector < std::vector<int> > m_summed_weights_for_rank;
+        std::vector < std::vector<unsigned> > m_summed_weights_for_rank;
 
     public:
         // The friend declaration gives the PowerupManager access to the