Don't call Store::setUp() unnecessarily

Fixes a threading issue with ESM::Land store caused by calling setUp() while it's being used.

apps/openmw/mwworld/store.cpp

@@ -607,6 +607,11 @@ namespace MWWorld
         }
         return ptr;
     }
+    void Store<ESM::Cell>::clearDynamic()
+    {
+        setUp();
+    }
+
     void Store<ESM::Cell>::setUp()
     {
         typedef DynamicExt::iterator ExtIterator;

apps/openmw/mwworld/store.hpp

@@ -293,6 +293,7 @@ namespace MWWorld
         const ESM::Cell *find(const std::string &id) const;
         const ESM::Cell *find(int x, int y) const;
 
+        virtual void clearDynamic();
         void setUp();
 
         RecordId load(ESM::ESMReader &esm);

apps/openmw/mwworld/worldimp.cpp

@@ -295,7 +295,6 @@ namespace MWWorld
         mWorldScene->clear();
 
         mStore.clearDynamic();
-        mStore.setUp();
 
         if (mPlayer)
         {