splice: don't generate zero-len segement bvecs

mainline inclusion
from mainline-v5.12-rc1
commit 0f1d344f
category: bugfix
bugzilla: 188445,https://gitee.com/openeuler/kernel/issues/I6J5NZ

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0f1d344feb534555a0dcd0beafb7211a37c5355e



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iter_file_splice_write() may spawn bvec segments with zero-length. In
preparation for prohibiting them, filter out by hand at splice level.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Yang Erkun <yangerkun@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>