Better fix for problem with empty database names in the mysql.db table

sql/sql_acl.cc

@@ -242,8 +242,11 @@ 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])
+    if (!db.db)
+    {
+      sql_print_error("Found an entry in the 'db' table with empty database name; Skipped");
       continue;
+    }
     db.user=get_field(&mem, table,2);
     db.access=get_access(table,3);
     db.access=fix_rights_for_db(db.access);