Ignore missing symlinks in fsUtils.traverseTreeSync()

These were previously throwing an error from the call to
statSync().

Now statSync() is wrapped in a try block and only performed when
lstatSync() reports a symbolic link.

spec/stdlib/fs-utils-spec.coffee

@@ -1,6 +1,7 @@
 fsUtils = require 'fs-utils'
 fs = require 'fs'
 path = require 'path'
+temp = require 'temp'
 
 describe "fsUtils", ->
   describe ".read(path)", ->
@@ -82,6 +83,14 @@ describe "fsUtils", ->
 
       expect(symlinkPaths).toEqual(paths)
 
+    it "ignores missing symlinks", ->
+      directory = temp.mkdirSync('symlink-in-here')
+      paths = []
+      onPath = (childPath) -> paths.push(childPath)
+      fs.symlinkSync(path.join(directory, 'source'), path.join(directory, 'destination'))
+      fsUtils.traverseTreeSync(directory, onPath)
+      expect(paths.length).toBe 0
+
   describe ".md5ForPath(path)", ->
     it "returns the MD5 hash of the file at the given path", ->
       expect(fsUtils.md5ForPath(require.resolve('fixtures/sample.js'))).toBe 'dd38087d0d7e3e4802a6d3f9b9745f2b'

src/stdlib/fs-utils.coffee

@@ -147,13 +147,16 @@ module.exports =
   makeTree: (directoryPath) ->
     mkdirp.sync(directoryPath) if directoryPath and not @exists(directoryPath)
 
-  traverseTreeSync: (rootPath, onFile, onDirectory) ->
+  traverseTreeSync: (rootPath, onFile, onDirectory=onFile) ->
     return unless @isDirectorySync(rootPath)
 
     traverse = (directoryPath, onFile, onDirectory) ->
       for file in fs.readdirSync(directoryPath)
         childPath = path.join(directoryPath, file)
-        stats = fs.statSync(childPath)
+        stats = fs.lstatSync(childPath)
+        if stats.isSymbolicLink()
+          try
+            stats = fs.statSync(childPath)
         if stats.isDirectory()
           traverse(childPath, onFile, onDirectory) if onDirectory(childPath)
         else if stats.isFile()