file descriptor and memory leak

[nbrachet]

I'm not quite sure how it happens but I believe when a layer has a TILEINDEX file msTiledSHPOpenFile() is called twice, once from the msQuery*() call, then again from the msLayerOpen() call.

Our exact sequence (from Java) is:

            int rc = layer.queryByPoint(map,
                                        point,
                                        mode,
                                        buffer);
            if (rc != MS_SUCCESS)
                return rc;

            rc = layer.open();
            if (rc != MS_SUCCESS)
                return rc;

            return MS_SUCCESS;

msTiledSHPOpenFile() blindly overwrites layer->layerinfo. Obviously when layer->layerinfo already points to a msTiledSHPLayerInfo and its opened file descriptors are leaked.

The attached patch is merely plugging the hole. The actual fix might be more complicated.