1. Binlog commit by rotate (MDEV-32014) should not be
    used with Galera, yet while WSREP binlog emulation
    is active, the code path could lead into
    binlog_cache_data::write_prepare() in an invalid
    state, leading to errors in MTR. To fix, an extra
    check is added to ensure the binlog is actually
    active before calling write_prepare().

 2. If the #binlog_cache_files directory exists on a
    mariadbd run without opt_log_bin, the directory
    was treated as a table/database, leading to errors.
    To fix, on startup, if opt_log_bin is disabled and
    #binlog_cache_files exists (in the default log
    directory), the directory is deleted (and an
    informational message is provided in the error
    log)

Reviewed By:
============
Andrei Elkin <andrei.elkin@mariadb.com>