fuse-uring: Avoid queue->stopped races and set/read that value under lock

In the Linux kernel, the following vulnerability has been resolved: fuse-uring: Avoid queue->stopped races and set/read that value under lock There are several readers of queue->stopped that check the value under lock, but fuse_uring_commit_fetch() did not and actually the value was not set under the lock in fuse_uring_abort_end_requests() either. Especially in fuse_uring_commit_fetch it is important to check under a lock, because due to races 'struct fuse_req' might be freed with fuse_request_end, but another thread/cpu might already do teardown work.