Fix for a security flaw in database hash

Docs/manual.texi

@@ -46928,6 +46928,8 @@ not yet 100% confident in this code.
 @appendixsubsec Changes in release 3.23.52
 @itemize @bullet
 @item
+Fixed  a security bug with empty db column in db table
+@item
 Changed initialisation of @code{RND()} to make it less predicatable.
 @item
 Fixed problem with @code{GROUP BY} on result with expression that created a

sql/sql_acl.cc

@@ -242,6 +242,8 @@ int  acl_init(bool dont_read_acl_tables)
     ACL_DB db;
     update_hostname(&db.host,get_field(&mem, table,0));
     db.db=get_field(&mem, table,1);
+    if (!db.db || !db.db[0])
+      continue;
     db.user=get_field(&mem, table,2);
     db.access=get_access(table,3);
     db.access=fix_rights_for_db(db.access);