Fix more AS sender ID thinkos.

Specifically, the ASes own user ID wasn't being treated as 'exclusive' so
a human could nab it. Also, the HS would needlessly send user queries to the
AS for its own user ID.

synapse/appservice/__init__.py

@@ -211,7 +211,10 @@ class ApplicationService(object):
         return self._matches_regex(room_id, ApplicationService.NS_ROOMS)
 
     def is_exclusive_user(self, user_id):
-        return self._is_exclusive(ApplicationService.NS_USERS, user_id)
+        return (
+            self._is_exclusive(ApplicationService.NS_USERS, user_id)
+            or user_id == self.sender
+        )
 
     def is_exclusive_alias(self, alias):
         return self._is_exclusive(ApplicationService.NS_ALIASES, alias)

synapse/handlers/appservice.py

@@ -180,7 +180,14 @@ class ApplicationServicesHandler(object):
             return
 
         user_info = yield self.store.get_user_by_id(user_id)
-        defer.returnValue(len(user_info) == 0)
+        if len(user_info) > 0:
+            defer.returnValue(False)
+            return
+
+        # user not found; could be the AS though, so check.
+        services = yield self.store.get_app_services()
+        service_list = [s for s in services if s.sender == user_id]
+        defer.returnValue(len(service_list) == 0)
 
     @defer.inlineCallbacks
     def _check_user_exists(self, user_id):