The bug was originally observed as hanging binlog background thread at
shutdown similar to one of MDEV-21120.
It occurred through unnessary xid logging in 1pc execution.
Two parts of the issue are fixed. Per engine loop by involved engine
with attempt to mark a group requiring xid unlogging gets corrected in
two ways. Do not execute it when the termination event is irrelevant
for recovery, does not have xid in particular. Do not break the loop
anymore unconditionally at the end of the 1st iteration.
