Fix skidding ai crash

src/items/item_manager.hpp

@@ -29,6 +29,8 @@
 #include <SColor.h>
 
 #include <assert.h>
+#include <algorithm>
+
 #include <map>
 #include <memory>
 #include <random>
@@ -174,6 +176,14 @@ public:
         return dynamic_cast<Item*>(m_all_items[n]);
     }
     // ------------------------------------------------------------------------
+    bool itemExists(const ItemState* is) const
+    {
+        if (!is)
+            return false;
+        auto it = std::find(m_all_items.begin(), m_all_items.end(), is);
+        return it != m_all_items.end();
+    }
+    // ------------------------------------------------------------------------
     /** Returns a reference to the array of all items on the specified quad.
      */
     const AllItemTypes& getItemsInQuads(unsigned int n) const

src/karts/controller/skidding_ai.cpp

@@ -222,6 +222,15 @@ unsigned int SkiddingAI::getNextSector(unsigned int index)
 void SkiddingAI::update(int ticks)
 {
     float dt = stk_config->ticks2Time(ticks);
+
+    // Clear stored items if they were deleted (for example a switched nitro)
+    if (m_item_to_collect &&
+        !ItemManager::get()->itemExists(m_item_to_collect))
+        m_item_to_collect = NULL;
+    if (m_last_item_random &&
+        !ItemManager::get()->itemExists(m_last_item_random))
+        m_last_item_random = NULL;
+
     m_controls->setRescue(false);
 
     // This is used to enable firing an item backwards.