Fixed File.file? for non-existent files

lib/fakefs.rb

@@ -128,7 +128,8 @@ module FakeFS
       if path.respond_to? :entry
         path.entry.is_a? MockFile
       else
-        FileSystem.find(path).entry.is_a? MockFile
+        result = FileSystem.find(path)
+        result && result.entry.is_a?(MockFile)
       end
     end
 

test/fakefs_test.rb

@@ -133,6 +133,10 @@ class FakeFSTest < Test::Unit::TestCase
     assert File.file?(sympath)
   end
 
+  def test_knows_non_existent_files_arent_files
+    assert ! File.file?('does/not/exist.txt')
+  end
+
   def test_can_chown_files
     good = 'file.txt'
     bad = 'nofile.txt'