title: Problems with MeshFaceMaterial since revision 54 (Update 2)
body: <p>Since I use revision 54 instead of revision 48 I get this excetption in my script:</p>
  
  <pre><code>Uncaught TypeError: Cannot read property 'map' of undefined three.js:18155
  bufferGuessUVType three.js:18155
  initMeshBuffers three.js:17963
  addObject three.js:21674
  initWebGLObjects three.js:21608
  render three.js:21145
  ...
  THREE.JSONLoader.createModel three.js:9892
  xhr.onreadystatechange
  </code></pre>
  
  <p>I am merging geometries with <code>THREE.GeometryUtils.merge</code>. Afterwards I use the merged geometry to construct a mesh. For this mesh I use <code>MeshFaceMaterial</code> to apply the materials of the faces. Since r54 this ends up in an exception. If I use some other material it works.. but then I can not use the materials of the original faces.</p>
  
  <p>Update: All faces are pointing to a material <code>geometry.faces[i].materialIndex</code> but geometries do not contain a material array any more. </p>
  
  <p>Update: 
  I just want to merge geometries and keep their materials :) I thought this would be the solution but the <code>materialIndex</code> of a face will not be update on merge. I post this example to somehow explain what I need.</p>
  
  <pre><code>mesh1 = new THREE.Mesh(new THREE.PlaneGeometry(2,2), new THREE.MeshBasicMaterial({ color: 0xFF0000}));
  mesh2 = new THREE.Mesh(new THREE.PlaneGeometry(2,2), new THREE.MeshBasicMaterial({ color: 0x0000FF}));
  mesh2.position.y = 3;
  THREE.GeometryUtils.merge(mergedGeo, mesh1);
  THREE.GeometryUtils.merge(mergedGeo, mesh2);
  scene.add(new THREE.Mesh(mergedGeo, new THREE.MeshFaceMaterial([mesh1.material, mesh2.material])));
  </code></pre>
  
  <p>I could implement an own logic to link the merged faces to the right material but this is a bit frustrating since it worked in earlier versions. </p>