Update TileLayer.GeoJSON.js
Update TileLayer.GeoJSON.js

When removing a layer while zooming, this._map might be null while _update would still be called
glenrobertson/leaflet-tilelayer-geojson,jgimbel/leaflet-tilelayer-geojson,kozer/leaflet-tilelayer-geojson,Livefyre/leaflet-tilelayer-geojson