vfs: move create error && negative dentry case in lookup_open() up

vfs: move create error && negative dentry case in lookup_open() up

O_CREAT is stripped when create_error is set in lookup_open(), so when
lookup does not return an inode, the case

	if (!dentry->d_inode && (open_flag & O_CREAT))

is always skipped. We can get rid of this cognitive step by handling the
error case first.

Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Jori Koolstra <jkoolstra@xs4all.nl>
Link: https://patch.msgid.link/20260710164233.827744-2-jkoolstra@xs4all.nl
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>