Check that env is not None before decrypting

After database migration 056, it became possible to have an environment
of None.  Check that env is not None before looking inside it.

Change-Id: Ic498e8e630608886178df83d1e7a503525834573
Closes-Bug: #1464379

heat/objects/raw_template.py

@@ -47,7 +47,8 @@ class RawTemplate(
             tpl[field] = db_tpl[field]
 
         # If any of the parameters were encrypted, then decrypt them
-        if env_fmt.ENCRYPTED_PARAM_NAMES in tpl.environment:
+        if (tpl.environment is not None and
+                env_fmt.ENCRYPTED_PARAM_NAMES in tpl.environment):
             parameters = tpl.environment[env_fmt.PARAMETERS]
             encrypted_param_names = tpl.environment[
                 env_fmt.ENCRYPTED_PARAM_NAMES]