[Backport #1817] bug of ARGF.eof?

Backport #1817: bug of ARGF.eof?
http://redmine.ruby-lang.org/issues/show/1817

e$B5/I<<Te(B: Nobuyoshi N.
e$B%9%F!<%?%9e(B: Assigned, e$BM%@hEYe(B: Normal
e$BC4Ev<Te(B: Yuki S., e$B%+%F%4%je(B: core

ARGF.eof?e$B$,:G=i$NFI$9~$$NA0$Ke(Btruee$B$rJV$7$F$$$^$7$?!#e(B
r24271e$B$G=$@5!#e(B

e$B%A%1%C%He(B #1817 e$B$,99?7$5$l$^$7$?!#e(B (by Yuki S.)

e$B%9%F!<%?%9e(B Assignede$B$+$ie(BClosede$B$KJQ99e(B

Applied in r24449.

http://redmine.ruby-lang.org/issues/show/1817