L.GeoJSON.asFeature should pass through FeatureCollections (#5049)

* L.GeoJSON.asFeature should pass through FeatureCollections

* Add unit test to verify FeatureCollection toGeoJSON

spec/suites/layer/LayerGroupSpec.js

@@ -68,4 +68,28 @@
 			}, ctx);
 		});
 	});
+
+	describe("#toGeoJSON", function () {
+		it('should return valid GeoJSON for a layer with a FeatureCollection', function () {
+			var geoJSON = {
+				"type":"FeatureCollection",
+				"features":[
+					{
+						"type":"Feature",
+						"properties":{},
+						"geometry": {
+							"type":"Point",
+							"coordinates": [78.3984375, 56.9449741808516]
+						}
+					}
+				]
+			};
+
+			var layerGroup = L.layerGroup();
+			var layer = L.geoJSON(geoJSON);
+			layerGroup.addLayer(layer);
+
+			L.geoJson(layerGroup.toGeoJSON());
+		});
+	});
 });

src/layer/GeoJSON.js

@@ -264,7 +264,7 @@ L.extend(L.GeoJSON, {
 	// @function asFeature(geojson: Object): Object
 	// Normalize GeoJSON geometries/features into GeoJSON features.
 	asFeature: function (geojson) {
-		if (geojson.type === 'Feature') {
+		if (geojson.type === 'Feature' || geojson.type === 'FeatureCollection') {
 			return geojson;
 		}