Support non texture.sampler specified glTF file

examples/js/loaders/GLTF2Loader.js

@@ -1430,16 +1430,12 @@ THREE.GLTF2Loader = ( function () {
 
 							_texture.type = texture.type !== undefined ? WEBGL_TEXTURE_DATATYPES[ texture.type ] : THREE.UnsignedByteType;
 
-							if ( texture.sampler !== undefined ) {
+							var sampler = texture.sampler === undefined ? {} : json.samplers[ texture.sampler ];
 
-								var sampler = json.samplers[ texture.sampler ];
-
-								_texture.magFilter = WEBGL_FILTERS[ sampler.magFilter ] || THREE.LinearFilter;
-								_texture.minFilter = WEBGL_FILTERS[ sampler.minFilter ] || THREE.NearestMipMapLinearFilter;
-								_texture.wrapS = WEBGL_WRAPPINGS[ sampler.wrapS ] || THREE.RepeatWrapping;
-								_texture.wrapT = WEBGL_WRAPPINGS[ sampler.wrapT ] || THREE.RepeatWrapping;
-
-							}
+							_texture.magFilter = WEBGL_FILTERS[ sampler.magFilter ] || THREE.LinearFilter;
+							_texture.minFilter = WEBGL_FILTERS[ sampler.minFilter ] || THREE.NearestMipMapLinearFilter;
+							_texture.wrapS = WEBGL_WRAPPINGS[ sampler.wrapS ] || THREE.RepeatWrapping;
+							_texture.wrapT = WEBGL_WRAPPINGS[ sampler.wrapT ] || THREE.RepeatWrapping;
 
 							resolve( _texture );