reflog: fix warning message.
reflog: fix warning message.

When ref@{N} is specified on a ref that has only M entries (M < N),
instead of saying the initial timestamp the reflog has, warn that
there is only M entries.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git