crimson/os/seastore/log_manager: return has_between result early for log keys

If the key is a log key, has_between() can determine the result by checking
whether the key is between the first and last entries. Return the result early
in this case.

Signed-off-by: Myoungwon Oh <ohmyoungwon@gmail.com>
Signed-off-by: Kefu Chai <k.chai@proxmox.com>