failed tc log preventing mariadb from starting - error message to be improved

I had the main disk partition full, and it seems that mariadb crashed, but when it tried to generate tc log, nothing more than a zero-length file was saved.

At next server start, mariadb couldn't start:

2018-10-10 21:13:01 139737626755648 [Note] Recovering after a crash using tc.log

2018-10-10 21:13:01 139737626755648 [ERROR] Can't init tc log

2018-10-10 21:13:01 139737626755648 [ERROR] Aborting

I had to manually delete /var/lib/mysql/tc.log

However, it seems a trivial change to let mariadb check tc.log's lenght before trying to init it, a 0-length tc.log can safely be deleted by mariadb and the server can start.