io_uring/kbuf: check for buffer list readiness after NULL check

stable inclusion
from stable-v6.6.7
commit 7e6621b99d20f26f7355a7f266bebd6f5ce88693
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8SSQ4

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7e6621b99d20f26f7355a7f266bebd6f5ce88693



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[ Upstream commit 9865346b7e8374b57f1c3ccacdc77846c6352ff4 ]

Move the buffer list 'is_ready' check below the validity check for
the buffer list for a given group.

Fixes: 5cf4f52e6d8a ("io_uring: free io_buffer_list entries via RCU")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>