Fix parsing of files without layer comps

examples/node/tree.js

@@ -2,6 +2,7 @@ var PSD = require('../../');
 
 var file = process.argv[2] || './examples/images/example.psd';
 
-PSD.open(file).then(function (psd) {
-  console.log(psd.tree().export());
-});
+var psd = PSD.fromFile(file);
+psd.parse();
+
\ No newline at end of file
+console.log(psd.tree().export());
\ No newline at end of file

lib/psd.coffee

+RSVP = require 'rsvp'
 {Module} = require 'coffeescript-module'
 
 File      = require './psd/file.coffee'
@@ -22,6 +23,8 @@ module.exports = class PSD extends Module
     Object.defineProperty @, 'layers',
       get: -> @layerMask.layers
 
+    RSVP.on 'error', (reason) -> console.error(reason)
+
   parse: ->
     return if @parsed
 

lib/psd/nodes/root.coffee

@@ -35,7 +35,7 @@ module.exports = class Root extends Node
       width: @width
       height: @height
       resources:
-        layerComps: @psd.resources.resource('layerComps').export()
+        layerComps: @psd.resources.resource('layerComps')?.export() or []
         guides: []
         slices: []