Fixed Inventory.get_hosts() ignoring restriction when there are no hosts left.

get_hosts() was treating [] (meaning complete restriction, no hosts allowed)
the same as None (meaning no restriction, all hosts allowed). Fixed logic.

lib/ansible/inventory/__init__.py

@@ -89,9 +89,10 @@ class Inventory(object):
              for host in group.get_hosts():
                  for pat in patterns:
                      if group.name == pat or pat == 'all' or self._match(host.name, pat):
-                         if not self._restriction:
+                         #must test explicitly for None because [] means no hosts allowed
+                         if self._restriction==None: 
                              hosts[host.name] = host
-                         if self._restriction and host.name in self._restriction:
+                         elif host.name in self._restriction:
                              hosts[host.name] = host
         return sorted(hosts.values(), key=lambda x: x.name)