TRUNCATE is not atomic after MDEV-13564

I observed this both on 10.2 and 10.3 when testing MDEV-13564. The following test would occasionally fail on a cmake -DCMAKE_BUILD_TYPE=Debug -DWITH_ASAN=1 build:

./mtr --parallel=40 --repeat=100 --mysqld=--debug=d,ib_log innodb.truncate_crash{,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,}

The reason for this appears to be that the following call does not always guarantee a write to the redo log:

log_write_up_to(mtr.commit_lsn(), true);

Such a call is present in all callers of fil_name_write_rename_low(), yet sometimes we end up with losing the table, because no undo log was persisted for the incomplete transaction despite this call.