jbd: abort instead of waiting for nonexistent transactions

The __log_wait_for_space function sits in a loop checkpointing
transactions until there is sufficient space free in the journal.
However, if there are no transactions to be processed (e.g.  because the
free space calculation is wrong due to a corrupted filesystem) it will
never progress.

Check for space being required when no transactions are outstanding and
abort the journal instead of endlessly looping.

This patch fixes the bug reported by Sami Liedes at:
http://bugzilla.kernel.org/show_bug.cgi?id=10976

Signed-off-by: Duane Griffin <duaneg@dghda.com>
Tested-by: Sami Liedes <sliedes@cc.hut.fi>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>