The ZIL may be failed any time we don't have the issuer lock, which
means we can end up working through zil_commit_impl() even when the ZIL
already failed.
So, each time we gain the issuer lock, recheck the fail state, and do
not issue IO if its failed. The waiter will eventually go to sleep
waiting to be signalled with the ZIL reopens in zil_sync()->zil_clean().
(cherry picked from commit 49fa92c8db389f257a15029d643fb026fa5b6dc2)
7121e678a2