Fix sometimes missing overworld background music

src/modes/overworld.cpp

@@ -124,10 +124,11 @@ void OverWorld::update(int ticks)
         setPhase(RACE_PHASE);
         // Normally done in WorldStatus::update(), during phase SET_PHASE,
         // so we have to start music 'manually', since we skip all phases.
+        MusicInformation* mi = Track::getCurrentTrack()->getTrackMusic();
         Track::getCurrentTrack()->startMusic();
 
         if (UserConfigParams::m_music)
-            music_manager->startMusic();
+            music_manager->startMusic(mi);
         m_karts[0]->startEngineSFX();
     }
     World::update(ticks);

src/tracks/track.cpp

@@ -176,6 +176,7 @@ Track::Track(const std::string &filename)
     m_minimap_y_scale       = 1.0f;
     m_force_disable_fog     = false;
     m_startup_run           = false;
+    m_music_idx             = 0;
     m_red_flag = m_blue_flag =
         btTransform(btQuaternion(0.0f, 0.0f, 0.0f, 1.0f));
     m_default_number_of_laps = 3;
@@ -709,6 +710,8 @@ void Track::getMusicInformation(std::vector<std::string>&       filenames,
             "Music information for track '%s' replaced by default music.\n",
             m_name.c_str());
     }
+    if (!m_music.empty())
+        m_music_idx = rand() % m_music.size();
 
 }   // getMusicInformation
 
@@ -719,7 +722,7 @@ void Track::startMusic() const
 {
     // In case that the music wasn't found (a warning was already printed)
     if(m_music.size()>0)
-        music_manager->startMusic(m_music[rand()% m_music.size()], false);
+        music_manager->startMusic(m_music[m_music_idx], false);
     else
         music_manager->clearCurrentMusic();
 }   // startMusic

src/tracks/track.hpp

@@ -118,6 +118,7 @@ private:
     std::string              m_screenshot;
     bool                     m_is_day;
     std::vector<MusicInformation*> m_music;
+    unsigned                       m_music_idx;
 
     /** Will only be used on overworld */
     std::vector<OverworldChallenge> m_challenges;
@@ -732,6 +733,13 @@ public:
     // ------------------------------------------------------------------------
     bool isOnGround(const Vec3& xyz, const Vec3& down, Vec3* hit_point,
                     Vec3* normal, bool print_warning = true);
+    // ------------------------------------------------------------------------
+    MusicInformation* getTrackMusic() const
+    {
+        if (m_music_idx < m_music.size())
+            return m_music[m_music_idx];
+        return NULL;
+    }
 };   // class Track
 
 #endif