cellpreloader: abort all tasks first before waiting

apps/openmw/mwworld/cellpreloader.cpp

@@ -198,10 +198,11 @@ namespace MWWorld
     CellPreloader::~CellPreloader()
     {
         for (PreloadMap::iterator it = mPreloadCells.begin(); it != mPreloadCells.end();++it)
-        {
             it->second.mWorkItem->abort();
+
+        for (PreloadMap::iterator it = mPreloadCells.begin(); it != mPreloadCells.end();++it)
             it->second.mWorkItem->waitTillDone();
-        }
+
         mPreloadCells.clear();
     }