Do not display public pages authored by deleted users

We check for both deleted and purged because their may be older galaxy
instances with user records that are purged but not deleted.

lib/galaxy/managers/pages.py

@@ -18,6 +18,7 @@
 
 import sqlalchemy
 from sqlalchemy import (
+    and_,
     desc,
     false,
     func,
@@ -168,6 +169,10 @@ def index_query(
             stmt = stmt.outerjoin(self.model_class.users_shared_with)
         stmt = stmt.where(or_(*filters))
 
+        # Do not include pages authored by deleted users
+        if show_published:
+            stmt = stmt.join(Page.user).where(and_(User.deleted == false(), User.purged == false()))
+
         if payload.user_id:
             stmt = stmt.where(self.model_class.user_id == payload.user_id)