NavMeshUpdateAll leak suppression (not 100% preventative)

1) Reset the build when adding potential dirties to the list to ensure it isn't trying to kill off a dirty entry that it's passed by.
2) mSaveIntermediates = true; causes leakage even with all this. still tracking that end.
3) Need to remove a dead tile whether there's new data to replace it with or not. Empty tiles are an entirely possible case. Even a probable one if you have high verticality in a level.
4) Likewise you don't want to re-feed the same geometry list for a given tile in case the conditions have changed.
5) If no vertcount then clear all geometry entries. (that one might be paranoia)

Engine/source/navigation/navMesh.cpp

@@ -113,7 +113,11 @@ DefineConsoleFunction(NavMeshUpdateAll, void, (S32 objid, bool remove), (0, fals
    for(U32 i = 0; i < set->size(); i++)
    {
       NavMesh *m = static_cast<NavMesh*>(set->at(i));
-      m->buildTiles(obj->getWorldBox());
+	   if (m)
+	   {
+         m->cancelBuild();
+         m->buildTiles(obj->getWorldBox());
+      }
    }
    if(remove)
       obj->enableCollision();
@@ -147,7 +151,7 @@ NavMesh::NavMesh()
    mFileName = StringTable->insert("");
    mNetFlags.clear(Ghostable);
 
-   mSaveIntermediates = true;
+   mSaveIntermediates = false;
    nm = NULL;
    ctx = NULL;
 
@@ -765,13 +769,15 @@ void NavMesh::buildNextTile()
       // Intermediate data for tile build.
       TileData tempdata;
       TileData &tdata = mSaveIntermediates ? mTileData[i] : tempdata;
+      
+      // Remove any previous data.
+      nm->removeTile(nm->getTileRefAt(tile.x, tile.y, 0), 0, 0);
+
       // Generate navmesh for this tile.
       U32 dataSize = 0;
       unsigned char* data = buildTileData(tile, tdata, dataSize);
       if(data)
       {
-         // Remove any previous data.
-         nm->removeTile(nm->getTileRefAt(tile.x, tile.y, 0), 0, 0);
          // Add new data (navmesh owns and deletes the data).
          dtStatus status = nm->addTile(data, dataSize, DT_TILE_FREE_DATA, 0, 0);
          int success = 1;
@@ -830,6 +836,7 @@ unsigned char *NavMesh::buildTileData(const Tile &tile, TileData &data, U32 &dat
    SceneContainer::CallbackInfo info;
    info.context = PLC_Navigation;
    info.boundingBox = box;
+   data.geom.clear();
    info.polyList = &data.geom;
    info.key = this;
    getContainer()->findObjects(box, StaticShapeObjectType | TerrainObjectType, buildCallback, &info);
@@ -843,8 +850,11 @@ unsigned char *NavMesh::buildTileData(const Tile &tile, TileData &data, U32 &dat
    }
 
    // Check for no geometry.
-   if(!data.geom.getVertCount())
-      return false;
+   if (!data.geom.getVertCount())
+   {
+      data.geom.clear();
+      return NULL;
+   }
 
    // Figure out voxel dimensions of this tile.
    U32 width = 0, height = 0;