only run gencode scripts if they exist

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>

lib/cdist/core/code.py

@@ -95,6 +95,7 @@ class Code(object):
     def _run_gencode(self, cdist_object, which):
         cdist_type = cdist_object.type
         script = os.path.join(self.local.type_path, getattr(cdist_type, 'gencode_%s_path' % which))
+        if os.path.isfile(script):
             env = os.environ.copy()
             env.update(self.env)
             env.update({