We don't currently test seeking from LLONG_MIN, which apparently can
produce an UBSAN warning, although I've been unable to reproduce
that. In any case, it's a good corner case to test and
straightforward to add.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Eryu Guan <guaneryu@gmail.com>