Don't start demo world wrongly when isNetworking is true in menu

Fix the weird abyss screenshot with tux in android

src/main_loop.cpp

@@ -159,7 +159,8 @@ float MainLoop::getLimitedDt()
         // when the computer can't keep it up, slow down the shown time instead
         // But this can not be done in networking, otherwise the game time on
         // client and server will not be in synch anymore
-        if(!NetworkConfig::get()->isNetworking())
+        if (!NetworkConfig::get()->isNetworking() ||
+           !World::getWorld())
         {
             /* time 3 internal substeps take */
             const float MAX_ELAPSED_TIME = 3.0f*1.0f / 60.0f*1000.0f;

src/modes/demo_world.cpp

@@ -28,9 +28,11 @@
 #include "tracks/track.hpp"
 #include "tracks/track_manager.hpp"
 
+#include <limits>
+
 std::vector<std::string> DemoWorld::m_demo_tracks;
 int                      DemoWorld::m_default_num_karts = 2;
-float                    DemoWorld::m_max_idle_time     = 99999.0f;
+float                    DemoWorld::m_max_idle_time     = std::numeric_limits<float>::max();
 float                    DemoWorld::m_current_idle_time = 0;
 bool                     DemoWorld::m_do_demo           = false;
 
@@ -104,6 +106,9 @@ void DemoWorld::enterRaceOverState()
  */
 bool DemoWorld::updateIdleTimeAndStartDemo(float dt)
 {
+    // Demo world is disabled if max float
+    if (m_max_idle_time == std::numeric_limits<float>::max())
+        return false;
     // We get crashes if stk is activated when a modal dialog is open
     if(GUIEngine::ModalDialog::isADialogActive())
         return false;