Fixes potential nullref exception on MultiGeometry

When the MultiGeometry object doesn't have a geometries child this caused
a crash. Shouldn't crash, should just result in an invalid geoJson.
Added a test for this.

index.js

@@ -146,7 +146,7 @@ var geometry = {
     },
     valid: function(_) {
         return _ && _.type && (_.coordinates ||
-            _.type === 'GeometryCollection' && _.geometries.every(geometry.valid));
+            _.type === 'GeometryCollection' && _.geometries && _.geometries.every(geometry.valid));
     },
     any: function(_) {
         if (geometry[_.type]) {

test/data/geometrycollection_nogeometries.geojson

@@ -0,0 +1,13 @@
+{ "type": "FeatureCollection",
+  "features": [{
+    "type": "Feature",
+    "geometry": { 
+      "type": "GeometryCollection"
+    },
+    "properties": {
+      "prop0": "value0",
+      "prop1": "val2"
+      }
+    }
+  ]
+}

test/data/geometrycollection_nogeometries.kml

@@ -0,0 +1 @@
+<?xml version="1.0" encoding="UTF-8"?><kml xmlns="http://www.opengis.net/kml/2.2"><Document></Document></kml>

test/kml.test.js

@@ -40,6 +40,7 @@ test('tokml', function(t) {
         geq(tt, 'multipoint');
         geq(tt, 'multipolygon');
         geq(tt, 'geometrycollection');
+        geq(tt, 'geometrycollection_nogeometries');
         tt.end();
     });
 
@@ -144,7 +145,7 @@ test('tokml', function(t) {
                 try {
                     tokml(gen);
                 } catch(e) {
-                    tt.fail('failed ' + JSON.stringify(gen) + 'with ' + e + e.stack);
+                    tt.fail('failed at fuzzed version of ' + gj + ': ' + JSON.stringify(gen) + 'with ' + e + e.stack);
                 }
             }
         });