fuse: check aborted connection before adding requests to pending list for resending

There is a race condition where inflight requests will not be aborted if
they are in the middle of being re-sent when the connection is aborted.

If fuse_resend has already moved all the requests in the fpq->processing
lists to its private queue ("to_queue") and then the connection starts
and finishes aborting, these requests will be added to the pending queue
and remain on it indefinitely.

Fixes: 760eac73 ("fuse: Introduce a new notification type for resend pending requests")
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Cc: <stable@vger.kernel.org> # v6.9
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>