There is a race condition in journal_write() where journal_lock is
being acquired after checking whether journal_fh is NULL or not.
journal_fh is a static file handle that can be set to NULL by any
other thread, while current thread is blocked by
pthread_mutex_lock(). This commit fixes this race condition.

Signed-off-by: Umer Saleem <usaleem@ixsystems.com>