Fix the character creation crash

When unloading a cell, the removeCell methods are destroying base nodes, but leave dangling pointers in RefData::mBaseNode. For non-disabled objects this does not matter, because they get new base nodes assigned to them anyway when the cell is loaded again. But disabled objects have their mBaseNode pointer unchanged, and when the cell is unloaded again, it will try to
 
         mPhysics->removeObject (node->getName());

with the dangling node pointer.
The quick fix is to make ListHandles also reset RefData::mBaseNode.