MDEV-31183 binlog_encryption.encrypted_master_switch_to_unencrypted_g…

…tid fails in BB with UBSAN runtime error: downcast of address

sql/log.cc:11101:56: runtime error: downcast of address 0x7f9dc801e9c8 which does not point to an object of type 'Gtid_list_log_event'
sql/sql_repl.cc:1429:12: runtime error: member call on address 0x7f1ca401ea48 which does not point to an object of type 'Gtid_list_log_event'

sql/log.cc

@@ -10788,7 +10788,7 @@ get_gtid_list_event(IO_CACHE *cache, Gtid_list_log_event **out_gtid_list)
       if (fdle->start_decryption((Start_encryption_log_event*) ev))
       {
         errormsg= "Could not set up decryption for binlog.";
-        break;
+        typ= UNKNOWN_EVENT; // to cleanup and abort below
       }
     }
     delete ev;